Converting time stamps in excel to dates

I have a very large excel spread sheet that has a column of time stamps. Does anyone know convert that over to a date? Is there a function I can use? I tried format cell date but that doesn't work. My file is 91,568 KB. If there is a simpler way to this that would be great. I'm open to ideas.

Thank you in advance :)

P.S. I don't know any programming languages

Use this formula and set formatting to the desired time format:

=(((COLUMN_ID_HERE/60)/60)/24)+DATE(1970,1,1)

Source: http://www.bajb.net/2010/05/excel-timestamp-to-date/ Tested in libreoffice

A timestamp is the elapsed time since Epoch time (01/01/1970), so basically we have to convert this time in days, and add the epoch time, to get a valid format for any Excel like spreadsheet software.

• From a timestamp in milliseconds (ex: 1488380243994)

  use this formula:

  =A1/1000/86400+25569
  

  with this formater:

  yyyy-mm-dd hh:mm:ss.000
  

• From a timestamp in seconds (ex: 1488380243)

  use this formula:

  =A1/86400+25569
  

  with this formater:

  yyyy-mm-dd hh:mm:ss
  

Where A1 is your column identifier. Given custom formaters allow to not loose precision in displayed data, but you can of course use any other date/time one that corresponds to your needs.

If you get a Error 509 in Libre office you may replace , by ; in the DATE() function

=(((COLUMN_ID_HERE/60)/60)/24)+DATE(1970;1;1)

below formula worked form me in MS EXEL

=TEXT(CELL_VALUE/24/60/60/1000 + 25569,"YYYY-MM-DD HH:MM")

CELL_VALUE is timestamp in milliseconds

here is explanation for text function.

If your file is really big try to use following formula: =A1 / 86400 + 25569

A1 should be replaced to what your need. Should work faster than =(((COLUMN_ID_HERE/60)/60)/24)+DATE(1970,1,1) cause of less number of calculations needed.