Excel and Google Sheets store dates as serial numbers, while Unix systems commonly store time as seconds or milliseconds since 1970-01-01 UTC. That difference is why a raw Unix value pasted into a spreadsheet looks like a large integer instead of a readable date. The correct formula divides the timestamp by the number of seconds in a day and then adds the spreadsheet date for January 1, 1970.
GeoTimeTools provides copy-ready formulas for the two formats you are most likely to receive. For a 10-digit seconds timestamp in cell A1, divide by 86400 and add DATE(1970,1,1). For a 13-digit millisecond timestamp, divide by 86400000 before adding the same base date. After entering the formula, format the result cell as yyyy-mm-dd hh:mm:ss to show both the date and the time.
The formulas are useful for support exports, analytics data, event logs, CSV cleanup, and spreadsheet-based audits. They work in Excel and Google Sheets because both use the same serial-date idea for this conversion. The page keeps seconds, milliseconds, and a timezone-adjustment example together, so you can choose the correct formula without searching through unrelated spreadsheet functions.
Seconds and milliseconds use different divisors
There are 86,400 seconds in a day, so seconds timestamps use 86400. There are 86,400,000 milliseconds in a day, so millisecond timestamps use 86400000. Using the wrong divisor creates a result that is off by a factor of 1,000.
Timezone adjustments need care
A Unix timestamp is anchored to UTC. A spreadsheet display may appear in a local timezone depending on the workflow, so document any manual offset you add. Use the timezone example as a starting point and confirm the daylight-saving rules for the region you are modelling.