[excel] Convert milliseconds to date (in Excel)

I have a row in excel with the following data: 1271664970687 (I think it's the number of milliseconds from 1970...). I would like to have addition row that will show it as date/time.

Converting your value in milliseconds to days is simply (MsValue / 86,400,000)

We can get 1/1/1970 as numeric value by DATE(1970,1,1)

= (MsValueCellReference / 86400000) + DATE(1970,1,1)

Using your value of 1271664970687 and formatting it as dd/mm/yyyy hh:mm:ss gives me a date and time of 19/04/2010 08:16:11

See Converting unix timestamp to excel date-time forum thread.