[iphone] How to calculate the width of a text string of a specific font and font-size?

I have a UILabel that displays some chars. Like "x", "y" or "rpm". How can I calculate the width of the text in the label (it does not ues the whole available space)? This is for automatic layouting, where another view will have a bigger frame rectangle if that UILabel has a smaller text inside. Are there methods to calculate that width of the text when a UIFont and font size is specified? There's also no line-break and just one single line.

This simple extension in Swift works well.

extension String {
    func size(OfFont font: UIFont) -> CGSize {
        return (self as NSString).size(attributes: [NSFontAttributeName: font])
    }
}

Usage:

let string = "hello world!"
let font = UIFont.systemFont(ofSize: 12)
let width = string.size(OfFont: font).width // size: {w: 98.912 h: 14.32}

Not sure how efficient this is, but I wrote this function that returns the point size that will fit a string to a given width:

func fontSizeThatFits(targetWidth: CGFloat, maxFontSize: CGFloat, font: UIFont) -> CGFloat {
    var variableFont = font.withSize(maxFontSize)
    var currentWidth = self.size(withAttributes: [NSAttributedString.Key.font:variableFont]).width

    while currentWidth > targetWidth {
        variableFont = variableFont.withSize(variableFont.pointSize - 1)
        currentWidth = self.size(withAttributes: [NSAttributedString.Key.font:variableFont]).width
    }

    return variableFont.pointSize
}

And it would be used like this:

textView.font = textView.font!.withSize(textView.text!.fontSizeThatFits(targetWidth: view.frame.width, maxFontSize: 50, font: textView.font!))

Swift 4

extension String {
    func SizeOf(_ font: UIFont) -> CGSize {
        return self.size(withAttributes: [NSAttributedStringKey.font: font])
    }
}

Update Sept 2019

This answer is a much cleaner way to do it using new syntax.

Original Answer

Based on Glenn Howes' excellent answer, I created an extension to calculate the width of a string. If you're doing something like setting the width of a UISegmentedControl, this can set the width based on the segment's title string.

extension String {

    func widthOfString(usingFont font: UIFont) -> CGFloat {
        let fontAttributes = [NSAttributedString.Key.font: font]
        let size = self.size(withAttributes: fontAttributes)
        return size.width
    }

    func heightOfString(usingFont font: UIFont) -> CGFloat {
        let fontAttributes = [NSAttributedString.Key.font: font]
        let size = self.size(withAttributes: fontAttributes)
        return size.height
    }

    func sizeOfString(usingFont font: UIFont) -> CGSize {
        let fontAttributes = [NSAttributedString.Key.font: font]
        return self.size(withAttributes: fontAttributes)
    }
}

usage:

    // Set width of segmentedControl
    let starString = "??"
    let starWidth = starString.widthOfString(usingFont: UIFont.systemFont(ofSize: 14)) + 16
    segmentedController.setWidth(starWidth, forSegmentAt: 3)

The way I am doing it my code is to make an extension of UIFont: (This is Swift 4.1)

extension UIFont {


    public func textWidth(s: String) -> CGFloat
    {
        return s.size(withAttributes: [NSAttributedString.Key.font: self]).width
    }

} // extension UIFont

This is for swift 2.3 Version. You can get the width of string.

var sizeOfString = CGSize()
if let font = UIFont(name: "Helvetica", size: 14.0)
    {
        let finalDate = "Your Text Here"
        let fontAttributes = [NSFontAttributeName: font] // it says name, but a UIFont works
        sizeOfString = (finalDate as NSString).sizeWithAttributes(fontAttributes)
    }

If you're struggling to get text width with multiline support, so you can use the next code (Swift 5):

func width(text: String, height: CGFloat) -> CGFloat {
    let attributes: [NSAttributedString.Key: Any] = [
        .font: UIFont.systemFont(ofSize: 17)
    ]
    let attributedText = NSAttributedString(string: text, attributes: attributes)
    let constraintBox = CGSize(width: .greatestFiniteMagnitude, height: height)
    let textWidth = attributedText.boundingRect(with: constraintBox, options: [.usesLineFragmentOrigin, .usesFontLeading], context: nil).width.rounded(.up)

    return textWidth
}

And the same way you could find text height if you need to (just switch the constraintBox implementation):

let constraintBox = CGSize(width: maxWidth, height: .greatestFiniteMagnitude)

Or here's a unified function to get text size with multiline support:

func labelSize(for text: String, maxWidth: CGFloat, maxHeight: CGFloat) -> CGSize {
    let attributes: [NSAttributedString.Key: Any] = [
        .font: UIFont.systemFont(ofSize: 17)
    ]

    let attributedText = NSAttributedString(string: text, attributes: attributes)

    let constraintBox = CGSize(width: maxWidth, height: maxHeight)
    let rect = attributedText.boundingRect(with: constraintBox, options: [.usesLineFragmentOrigin, .usesFontLeading], context: nil).integral

    return rect.size
}

Usage:

let textSize = labelSize(for: "SomeText", maxWidth: contentView.bounds.width, maxHeight: .greatestFiniteMagnitude)
let textHeight = textSize.height.rounded(.up)
let textWidth = textSize.width.rounded(.up)

Swift-5

Use intrinsicContentSize to find the text height and width.

yourLabel.intrinsicContentSize.width

This will work even you have custom spacing between your string like "T E X T"

Since sizeWithFont is deprecated, I'm just going to update my original answer to using Swift 4 and .size

//: Playground - noun: a place where people can play

import UIKit

if let font = UIFont(name: "Helvetica", size: 24) {
   let fontAttributes = [NSAttributedStringKey.font: font]
   let myText = "Your Text Here"
   let size = (myText as NSString).size(withAttributes: fontAttributes)
}

The size should be the onscreen size of "Your Text Here" in points.

Oneliner in Swift 4.2

let size = text.size(withAttributes:[.font: UIFont.systemFont(ofSize:18.0)])

sizeWithFont: is now deprecated, use sizeWithAttributes: instead:

UIFont *font = [UIFont fontWithName:@"Helvetica" size:30];
NSDictionary *userAttributes = @{NSFontAttributeName: font,
                                 NSForegroundColorAttributeName: [UIColor blackColor]};
NSString *text = @"hello";
...
const CGSize textSize = [text sizeWithAttributes: userAttributes];

For Swift 3.0+

extension String {
    func SizeOf_String( font: UIFont) -> CGSize {
        let fontAttribute = [NSFontAttributeName: font]
        let size = self.size(attributes: fontAttribute)  // for Single Line
       return size;
   }
}

Use it like...

        let Str = "ABCDEF"
        let Font =  UIFont.systemFontOfSize(19.0)
        let SizeOfString = Str.SizeOfString(font: Font!)