Unix time is defined as the number of seconds since midnight (GMT time) on January 1, 1970 – also known as the Unix epoch.

For example, here's the Unix timestamp for August 4, 2008 at 10:19:08 pm (GMT):

1217888348

To create an Excel formula to convert a Unix timestamp to a readable data and time, start by converting the seconds to days. This formula assumes that the Unix timestamp is in cell A1:

''(((A1/60)/60)/24)

Then, you need to add the result to the date value for January 1, 1970. The modified formula is:

''(((A1/60)/60)/24)+DATE(1970,1,1)

Finally, you need to adjust the formula for the GMT offset. For example, if you're in New York the GMT offset is -5. Therefore, the final formula is:

''(((A1/60)/60)/24)+DATE(1970,1,1)+(-5/24)

A simpler (but much less clear) formula that returns the same result is:

''(A1/86400)+25569+(-5/24)

Both of these formulas return a date/time serial number, so you need to apply a number format to make it readable as a date and time.

– Main.FredPettis - 2011-02-15