How to round a number to n decimal places in Java

Question

What I would like is a method to convert a double to a string which rounds using the half-up method - i e  if the decimal to be rounded is 5  it always rounds up to the next number  This is the standard method of rounding most people expect in most situations   I also would like only significant digits to be displayed - i e  there should not be any trailing zeroes   I know one method of doing this is to use the String format method   String format    5g n   0 912385     returns   0 91239   which is great  however it always displays numbers with 5 decimal places even if they are not significant    String format    5g n   0 912300     returns   0 91230   Another method is to use the DecimalFormatter   DecimalFormat df   new DecimalFormat             df format 0 912385     returns   0 91238   However as you can see this uses half-even rounding  That is it will round down if the previous digit is even  What I d like is this   0 912385 - gt  0 91239 0 912300 - gt  0 9123   What is the best way to achieve this in Java

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If you re using a technology that has a minimal JDK   Here s a way without any Java libs   double scale   100000      double myVal   0 912385  double rounded    int   myVal   scale    0 5d    scale

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Try this  org apache commons math3 util Precision round double x  int scale   See  http   commons apache org proper commons-math apidocs org apache commons math3 util Precision html  Apache Commons Mathematics Library homepage is  http   commons apache org proper commons-math index html  The internal implemetation of this method is   public static double round double x  int scale        return round x  scale  BigDecimal ROUND HALF UP      public static double round double x  int scale  int roundingMethod        try           return  new BigDecimal                 Double toString x                   setScale scale  roundingMethod                   doubleValue          catch  NumberFormatException ex            if  Double isInfinite x                 return x            else               return Double NaN

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If you really want decimal numbers for calculation  and not only for output   do not use a binary-based floating point format like double   Use BigDecimal or any other decimal-based format    I do use BigDecimal for calculations  but bear in mind it is dependent on the size of numbers you re dealing with   In most of my implementations  I find parsing from double or integer to Long is sufficient enough for very large number calculations   In fact  I ve recently used parsed-to-Long to get accurate representations  as opposed to hex results  in a GUI for numbers as big as                                   characters  as an  example

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here is my answer   double num   4 898979485566356  DecimalFormat df   new DecimalFormat                time   Double valueOf df format num     System out println num      4 89

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You can also use the   DecimalFormat df   new DecimalFormat    00000    df format 0 912385     to make sure you have the trailing 0 s

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You can use the DecimalFormat class   double d   3 76628729   DecimalFormat newFormat   new DecimalFormat          double twoDecimal    Double valueOf newFormat format d

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So after reading most of the answers  I realized most of them won t be precise  in fact using BigDecimal seems like the best choice  but if you don t understand how the RoundingMode works  you will inevitable lose precision  I figured this out when working with big numbers in a project and thought it could help others having trouble rounding numbers  For example   BigDecimal bd   new BigDecimal  1363 2749    bd   bd setScale 2  RoundingMode HALF UP   System out println bd doubleValue       You would expect to get 1363 28 as an output  but you will end up with 1363 27  which is not expected  if you don t know what the RoundingMode is doing  So looking into the Oracle Docs  you will find the following description for RoundingMode HALF UP      Rounding mode to round towards  nearest neighbor  unless both   neighbors are equidistant  in which case round up    So knowing this  we realized that we won t be getting an exact rounding  unless we want to round towards nearest neighbor  So  to accomplish an adequate round  we would need to loop from the n-1 decimal towards the desired decimals digits  For example   private double round double value  int places  throws IllegalArgumentException        if  places  lt  0  throw new IllegalArgumentException            Cast the number to a String and then separate the decimals      String stringValue   Double toString value       String decimals   stringValue split        1           Round all the way to the desired number      BigDecimal bd   new BigDecimal stringValue       for  int i   decimals length  -1  i  gt   places  i--            bd   bd setScale i  RoundingMode HALF UP              return bd doubleValue        This will end up giving us the expected output  which would be 1363 28

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As some others have noted  the correct answer is to use either DecimalFormat or BigDecimal  Floating-point doesn t have decimal places so you cannot possibly round truncate to a specific number of them in the first place  You have to work in a decimal radix  and that is what those two classes do   I am posting the following code as a counter-example to all the answers in this thread and indeed all over StackOverflow  and elsewhere  that recommend multiplication followed by truncation followed by division  It is incumbent on advocates of this technique to explain why the following code produces the wrong output in over 92  of cases   public class RoundingCounterExample        static float roundOff float x  int position                float a   x          double temp   Math pow 10 0  position           a    temp          a   Math round a           return  a    float temp              public static void main String   args                float a   roundOff 0 0009434f 3           System out println  a   a    a    001     a   0 001            int count   0  errors   0          for  double x   0 0  x  lt  1  x    0 0001                        count                double d   x              int scale   2              double factor   Math pow 10  scale               d   Math round d   factor    factor              if   d   0 01     0 0                                System out println d          d   0 01                    errors                                    System out println count     trials     errors     errors              Output of this program   10001 trials 9251 errors   EDIT  To address some comments below I redid the modulus part of the test loop using BigDecimal and new MathContext 16  for the modulus operation as follows   public static void main String   args        int count   0  errors   0      int scale   2      double factor   Math pow 10  scale       MathContext mc   new MathContext 16  RoundingMode DOWN       for  double x   0 0  x  lt  1  x    0 0001                count            double d   x          d   Math round d   factor    factor          BigDecimal bd   new BigDecimal d  mc           bd   bd remainder new BigDecimal  0 01    mc           if  bd multiply BigDecimal valueOf 100   remainder BigDecimal ONE  mc  compareTo BigDecimal ZERO     0                        System out println d         bd               errors                        System out println count     trials     errors     errors        Result   10001 trials 4401 errors

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Milhous  the decimal format for rounding is excellent      You can also use the   DecimalFormat df   new DecimalFormat    00000    df format 0 912385         to make sure you have the trailing 0 s    I would add that this method is very good at providing an actual numeric  rounding mechanism - not only visually  but also when processing   Hypothetical  you have to implement a rounding mechanism into a GUI program  To alter the accuracy   precision of a result output simply  change the caret format  i e  within the brackets    So that   DecimalFormat df   new DecimalFormat   0           df format 0 912385     would return as output  0 912385  DecimalFormat df   new DecimalFormat   0          df format 0 912385     would return as output  0 91239  DecimalFormat df   new DecimalFormat   0         df format 0 912385     would return as output  0 9124   EDIT  also if the caret format is like so    0                and you enter a decimal  e g  3 1415926  for argument s sake  DecimalFormat does not produce any garbage  e g  trailing zeroes  and will return  3 1415926    if you re that way inclined  Granted  it s a little verbose for the liking of some dev s - but hey  it s got a low memory footprint during processing and is very easy to implement    So essentially  the beauty of DecimalFormat is that it simultaneously handles the string  appearance - as well as the level of rounding precision set  Ergo  you  get two benefits for the price of one code implementation

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double myNum    912385  int precision   10000    keep 4 digits myNum  Math floor myNum   precision   5  precision

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public static double formatDecimal double amount        BigDecimal amt   new BigDecimal amount       amt   amt divide new BigDecimal 1   2  BigDecimal ROUND HALF EVEN       return amt doubleValue       Test using Junit  RunWith Parameterized class  public class DecimalValueParameterizedTest       Parameterized Parameter   public double amount      Parameterized Parameter 1    public double expectedValue    Parameterized Parameters public static List lt Object   gt  dataSets         return Arrays asList new Object                   1000 0  1000 0                1000  1000 0                1000 00000  1000 0                1000 01  1000 01                1000 1  1000 10                1000 001  1000 0                1000 005  1000 0                1000 007  1000 01                1000 999  1001 0                1000 111  1000 11              Test public void testDecimalFormat         Assert assertEquals expectedValue  formatDecimal amount   0 00

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I have used bellow like in java 8  it is working for me      double amount   1000 431              NumberFormat formatter   new DecimalFormat     00        String output   formatter format amount       System out println  output       output     Output   output   1000 43

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the following method could be used if need double double getRandom int decimalPoints        double a   Math random        int multiplier    int  Math pow 10  decimalPoints       int b    int   a   multiplier       return b    double  multiplier     for example getRandom 2

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If you Consider 5 or n number of decimal  May be this answer solve your prob       double a   123 00449      double roundOff1   Math round a 10000  10000 00      double roundOff2   Math round roundOff1 1000  1000 00      double roundOff   Math round roundOff2 100  100 00       System out println  result   roundOff     Output will be  123 01 this can be solve with loop and recursive function

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Assuming value is a double  you can do    double Math round value   100000d    100000d   That s for 5 digits precision  The number of zeros indicate the number of decimals

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Here is a better function that rounds edge cases like 1 005 correctly  Simply  we add the smallest possible float value    1 ulp  unit in the last place  to the number before rounding  This moves to the next representable value after the number  away from zero  This is a little program to test it  ideone com        Round half away from zero   commercial  rounding     Uses correction to offset floating-point inaccuracies     Works symmetrically for positive and negative numbers      public static double round double num  int digits            epsilon correction     double n   Double longBitsToDouble Double doubleToLongBits num    1       double p   Math pow 10  digits       return Math round n   p    p        test rounding of half System out println round 0 5  0         1 System out println round -0 5  0        -1     testing edge cases System out println round 1 005  2         1 01 System out println round 2 175  2         2 18 System out println round 5 015  2         5 02  System out println round -1 005  2        -1 01 System out println round -2 175  2        -2 18 System out println round -5 015  2        -5 02

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Keep in mind that String format   and DecimalFormat produce string using default Locale  So they may write formatted number with dot or comma as a separator between integer and decimal parts  To make sure that rounded String is in the format you want use java text NumberFormat as so     Locale locale   Locale ENGLISH    NumberFormat nf   NumberFormat getNumberInstance locale        for trailing zeros    nf setMinimumFractionDigits 2        round to 2 digits    nf setMaximumFractionDigits 2      System out println nf format  99      System out println nf format 123 567      System out println nf format 123 0      Will print in English locale  no matter what your locale is     0 99   123 57   123 00  The example is taken from Farenda - how to convert double to String correctly

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Use setRoundingMode  set the RoundingMode explicitly to handle your issue with the half-even round  then use the format pattern for your required output   Example   DecimalFormat df   new DecimalFormat            df setRoundingMode RoundingMode CEILING   for  Number n   Arrays asList 12  123 12345  0 23  0 1  2341234 212431324         Double d   n doubleValue        System out println df format d        gives the output   12 123 1235 0 23 0 1 2341234 2125     EDIT  The original answer does not address the accuracy of the double values  That is fine if you don t care much whether it rounds up or down  But if you want accurate rounding  then you need to take the expected accuracy of the values into account  Floating point values have a binary representation internally  That means that a value like 2 7735 does not actually have that exact value internally  It can be slightly larger or slightly smaller  If the internal value is slightly smaller  then it will not round up to 2 7740  To remedy that situation  you need to be aware of the accuracy of the values that you are working with  and add or subtract that value before rounding  For example  when you know that your values are accurate up to 6 digits  then to round half-way values up  add that accuracy to the value   Double d   n doubleValue     1e-6    To round down  subtract the accuracy

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Here is a summary of what you can use if you want the result as String    DecimalFormat setRoundingMode     DecimalFormat df   new DecimalFormat             df setRoundingMode RoundingMode HALF UP   String str1   df format 0 912385       0 91239  BigDecimal setScale    String str2   new BigDecimal 0 912385       setScale 5  BigDecimal ROUND HALF UP       toString       Here is a suggestion of what libraries you can use if you want double as a result  I wouldn t recommend it for string conversion  though  as double may not be able to represent what you want exactly  see e g  here     Precision from Apache Commons Math   double rounded   Precision round 0 912385  5  BigDecimal ROUND HALF UP    Functions from Colt  double rounded   Functions round 0 00001  apply 0 912385   Utils from Weka  double rounded   Utils roundDouble 0 912385  5

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A simple way to compare if it is limited number of decimal places  Instead of DecimalFormat  Math or BigDecimal  we can use Casting  Here is the sample  public static boolean threeDecimalPlaces double value1  double value2       boolean isEqual   false         value1   3 1756         value2   3 17        int   value1   1000    3175        int   value2   1000    3170      if   int   value1   1000      int   value2   1000            areEqual   true             return isEqual

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You can use BigDecimal  BigDecimal value   new BigDecimal  2 3    value   value setScale 0  RoundingMode UP   BigDecimal value1   new BigDecimal  -2 3    value1   value1 setScale 0  RoundingMode UP   System out println value    n    value1     Refer  http   www javabeat net precise-rounding-of-decimals-using-rounding-mode-enumeration

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Real s Java How-to posts this solution  which is also compatible for versions before Java 1 6  BigDecimal bd   new BigDecimal Double toString d    bd   bd setScale decimalPlace  BigDecimal ROUND HALF UP   return bd doubleValue     UPDATE  BigDecimal ROUND HALF UP is deprecated - Use RoundingMode BigDecimal bd   new BigDecimal Double toString number    bd   bd setScale decimalPlaces  RoundingMode HALF UP   return bd doubleValue

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Suppose you have  double d   9232 129394d    you can use BigDecimal  BigDecimal bd   new BigDecimal d  setScale 2  RoundingMode HALF EVEN   d   bd doubleValue      or without BigDecimal   d   Math round d 100  100 0d    with both solutions d    9232 13

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I agree with the chosen answer to use DecimalFormat --- or alternatively BigDecimal   Please read Update below first   However if you do want to round the double value and get a double value result  you can use org apache commons math3 util Precision round     as mentioned above  The implementation uses BigDecimal  is slow and creates garbage   A similar but fast and garbage-free method is provided by the DoubleRounder utility in the decimal4j library    double a   DoubleRounder round 2 0 3 0  3    double b   DoubleRounder round 2 0 3 0  3  RoundingMode DOWN    double c   DoubleRounder round 1000 0d  17    double d   DoubleRounder round 90080070060 1d  9    System out println a    System out println b    System out println c    System out println d     Will output   0 667  0 666  1000 0  9 00800700601E10   See https   github com tools4j decimal4j wiki DoubleRounder-Utility  Disclaimer  I am involved in the decimal4j project   Update  As  iaforek pointed out DoubleRounder sometimes returns counterintuitive results  The reason is that it performs mathematically correct rounding  For instance DoubleRounder round 256 025d  2  will be rounded down to 256 02 because the double value represented as 256 025d is somewhat smaller than the rational value 256 025 and hence will be rounded down    Notes    This behaviour is very similar to that of the BigDecimal double  constructor  but not to valueOf double  which uses the string constructor   The problem can be circumvented with a double rounding step to a higher precision first  but it is complicated and I am not going into the details here   For those reasons and everything mentioned above in this post I cannot recommend to use DoubleRounder

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The code snippet below shows how to display n digits   The trick is to set variable pp to 1 followed by n zeros   In the example below  variable pp value has 5 zeros  so 5 digits will be displayed   double pp   10000   double myVal   22 268699999999967  String needVal    22 2687    double i    5 0 pp    String format     10 4f   String getVal   String format format  Math round  myVal  i  pp  pp -i  trim

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new BigDecimal String valueOf double   setScale yourScale  BigDecimal ROUND HALF UP     will get you a BigDecimal   To get the string out of it  just call that BigDecimal s toString method  or the toPlainString method for Java 5  for a plain format string     Sample program     package trials  import java math BigDecimal   public class Trials        public static void main String   args            int yourScale   10          System out println BigDecimal valueOf 0 42344534534553453453-0 42324534524553453453  setScale yourScale  BigDecimal ROUND HALF UP

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You could use the following utility method-  public static double round double valueToRound  int numberOfDecimalPlaces        double multipicationFactor   Math pow 10  numberOfDecimalPlaces       double interestedInZeroDPs   valueToRound   multipicationFactor      return Math round interestedInZeroDPs    multipicationFactor

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Just in case someone still needs help with this  This solution works perfectly for me   private String withNoTrailingZeros final double value  final int nrOfDecimals    return new BigDecimal String valueOf value   setScale nrOfDecimals   BigDecimal ROUND HALF UP  stripTrailingZeros   toPlainString         returns a  String  with the desired output

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In order to have trailing 0s up to 5th position   DecimalFormat decimalFormatter   new DecimalFormat  quot   00000 quot    decimalFormatter format 0 350500      result 0 350500    In order to avoid trailing 0s up to 5th position   DecimalFormat decimalFormatter  new DecimalFormat  quot         quot    decimalFormatter format 0 350500      result o 3505

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Where dp   decimal place you want  and value is a double       double p   Math pow 10d  dp        double result   Math round value   p  p

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A succinct solution      public static double round double value  int precision          int scale    int  Math pow 10  precision         return  double  Math round value   scale    scale        See also  https   stackoverflow com a 22186845 212950 Thanks to jpdymond for offering this

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To achieve this we can use this formatter    DecimalFormat df   new DecimalFormat    00     String resultado   df format valor    or   DecimalFormat df   new DecimalFormat  0 00        Use this method to get always two decimals      private static String getTwoDecimals double value         DecimalFormat df   new DecimalFormat  0 00           return df format value             Defining this values   91 32 5 22 11 5 1 2 2 6   Using the method we can get this results   91 32 5 22 11 50 1 20 2 60   demo online

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DecimalFormat is the best ways to output  but I don t prefer it  I always do this all the time  because it return the double value  So I can use it  more than just output   Math round selfEvaluate 100000d 0  100000d 0    OR  Math round selfEvaluate 100000d 0  0 00000d1    If you need large decimal places value  you can use BigDecimal instead  Anyways  0 is important  Without it the rounding of 0 33333d5 return 0 33333 and only 9 digits are allows  The second function without  0 has problems with 0 30000 return 0 30000000000000004

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I came here just wanting a simple answer on how to round a number  This is a supplemental answer to provide that   How to round a number in Java  The most common case is to use Math round     Math round 3 7     4   Numbers are rounded to the nearest whole number  A  5 value is rounded up  If you need different rounding behavior than that  you can use one of the other Math functions  See the comparison below   round  As stated above  this rounds to the nearest whole number   5 decimals round up   This method returns an int   Math round 3 0      3 Math round 3 1      3 Math round 3 5      4 Math round 3 9      4  Math round -3 0      -3 Math round -3 1      -3 Math round -3 5      -3     careful here     Math round -3 9      -4   ceil  Any decimal value is rounded up to the next integer  It goes to the ceiling  This method returns a double   Math ceil 3 0      3 0 Math ceil 3 1      4 0 Math ceil 3 5      4 0 Math ceil 3 9      4 0  Math ceil -3 0      -3 0 Math ceil -3 1      -3 0 Math ceil -3 5      -3 0 Math ceil -3 9      -3 0   floor  Any decimal value is rounded down to the next integer  This method returns a double   Math floor 3 0      3 0 Math floor 3 1      3 0 Math floor 3 5      3 0 Math floor 3 9      3 0  Math floor -3 0      -3 0 Math floor -3 1      -4 0 Math floor -3 5      -4 0 Math floor -3 9      -4 0   rint  This is similar to round in that decimal values round to the closest integer  However  unlike round   5 values round to the even integer   This method returns a double   Math rint 3 0      3 0 Math rint 3 1      3 0 Math rint 3 5      4 0     Math rint 3 9      4 0 Math rint 4 5      4 0     Math rint 5 5      6 0      Math rint -3 0      -3 0 Math rint -3 1      -3 0 Math rint -3 5      -4 0     Math rint -3 9      -4 0 Math rint -4 5      -4 0     Math rint -5 5      -6 0

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Since I found no complete answer on this theme I ve put together a class that should handle this properly  with support for    Formatting  Easily format a double to string with a certain number of decimal places Parsing  Parse the formatted value back to double Locale  Format and parse using the default locale Exponential notation  Start using exponential notation after a certain threshold   Usage is pretty simple    For the sake of this example I am using a custom locale   public static final int DECIMAL PLACES   2   NumberFormatter formatter   new NumberFormatter DECIMAL PLACES    String value   formatter format 9 319       9 32  String value2   formatter format 0 0000005       5 00E-7  String value3   formatter format 1324134123       1 32E9   double parsedValue1   formatter parse  0 4E-2   0      0 004 double parsedValue2   formatter parse  0 002   0      0 002 double parsedValue3   formatter parse  3423 12345   0      3423 12345   Here is the class   import java math RoundingMode  import java text DecimalFormat  import java text DecimalFormatSymbols  import java text ParseException  import java util Locale   public class NumberFormatter        private static final String SYMBOL INFINITE               u221e       private static final char   SYMBOL MINUS                 -       private static final char   SYMBOL ZERO                  0       private static final int    DECIMAL LEADING GROUPS      10      private static final int    EXPONENTIAL INT THRESHOLD   1000000000     After this value switch to exponential notation     private static final double EXPONENTIAL DEC THRESHOLD   0 0001     Below this value switch to exponential notation      private DecimalFormat decimalFormat      private DecimalFormat decimalFormatLong      private DecimalFormat exponentialFormat       private char groupSeparator       public NumberFormatter int decimalPlaces            configureDecimalPlaces decimalPlaces              public void configureDecimalPlaces int decimalPlaces            if  decimalPlaces  lt   0                throw new IllegalArgumentException  Invalid decimal places                       DecimalFormatSymbols separators   new DecimalFormatSymbols Locale getDefault             separators setMinusSign SYMBOL MINUS           separators setZeroDigit SYMBOL ZERO            groupSeparator   separators getGroupingSeparator             StringBuilder decimal   new StringBuilder            StringBuilder exponential   new StringBuilder  0              for  int i   0  i  lt  DECIMAL LEADING GROUPS  i                  decimal append        append i    DECIMAL LEADING GROUPS - 1                                  for  int i   0  i  lt  decimalPlaces  i                  decimal append                   exponential append  0                       exponential append  E0             decimalFormat   new DecimalFormat decimal toString    separators           decimalFormatLong   new DecimalFormat decimal append         toString    separators           exponentialFormat   new DecimalFormat exponential toString    separators            decimalFormat setRoundingMode RoundingMode HALF UP           decimalFormatLong setRoundingMode RoundingMode HALF UP           exponentialFormat setRoundingMode RoundingMode HALF UP              public String format double value            String result          if  Double isNaN value                 result                 else if  Double isInfinite value                 result   String valueOf SYMBOL INFINITE             else               double absValue   Math abs value               if  absValue  gt   1                    if  absValue  gt   EXPONENTIAL INT THRESHOLD                        value   Math floor value                       result   exponentialFormat format value                     else                       result   decimalFormat format value                                   else if  absValue  lt  1  amp  amp  absValue  gt  0                    if  absValue  gt   EXPONENTIAL DEC THRESHOLD                        result   decimalFormat format value                       if  result equalsIgnoreCase  0                              result   decimalFormatLong format value                                           else                       result   exponentialFormat format value                                   else                   result    0                                   return result             public String formatWithoutGroupSeparators double value            return removeGroupSeparators format value               public double parse String value  double defValue            try               return decimalFormat parse value  doubleValue              catch  ParseException e                e printStackTrace                      return defValue             private String removeGroupSeparators String number            return number replace String valueOf groupSeparator

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If you re using DecimalFormat to convert double to String  it s very straightforward   DecimalFormat formatter   new DecimalFormat  0 0      formatter setRoundingMode RoundingMode HALF UP    double num   1 234567  return formatter format num     There are several RoundingMode enum values to select from  depending upon the behaviour you require

[java] How to round a number to n decimal places in Java

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