Convert Unix timestamps

How to use it#

1. Paste a timestamp, or click Use current time to start from now.
2. If the number is close to 1970, set the unit rather than leaving it on Auto.
3. Switch between your zone and UTC to reread the same instant, then copy the row you need.

Seconds, milliseconds, and how to tell them apart#

A Unix timestamp counts from midnight UTC on 1 January 1970. Unix itself, and most databases and APIs, count in seconds. JavaScript counts in milliseconds, which is the single most common cause of a date landing in 1970 or in the year 54,000.

Length is the quick test. A current timestamp in seconds has ten digits; in milliseconds it has thirteen. That rule holds from 2001 until 2286, which covers anything you are likely to be debugging.

The rule breaks for dates near the epoch itself, where a seconds value has far fewer digits and could plausibly be either. Auto detection here guesses by magnitude and gets it right for any modern date, but the unit is a setting you can override precisely because the guess is not always right.

Why the readable time depends on where you are#

A timestamp has no time zone. It is a count of seconds since a fixed instant, and it means the same moment everywhere on earth. The zone only matters when you turn it into something a person reads, because that is when the clock on the wall gets involved.

The two readable rows on this page show the same instant twice. Switching between them changes nothing about the underlying value, which is why the Unix and ISO rows do not move when you toggle it. If a bug report and a log file disagree about when something happened, this is usually where the disagreement lives.

ISO 8601 with a trailing Z is the safest thing to write down, because it is unambiguous and sorts correctly as plain text. A date written as 03/04/2023 is not, and which of March and April it means depends on who typed it.

The 2038 problem, briefly#

Systems that store a timestamp as a signed 32-bit integer run out of room on 19 January 2038, when the count exceeds 2,147,483,647 and wraps to a negative number near 1901. It is the same shape of problem as Y2K and it is still present in older embedded systems and some database columns.

Modern languages use 64-bit values and are unaffected. If you maintain something that stores epoch seconds in a 32-bit column, that column is the thing to find, and the fix is widening it rather than doing anything clever with the values already in it.