How does it tell seconds from milliseconds?

By size. A ten-digit number such as 1756166400 is below the cutoff and is read as seconds, while a thirteen-digit number is above it and is read as milliseconds. Pick Seconds or Milliseconds in the Unit menu to override the guess.

Which time zone is used when my date has none?

A date with a time but no zone is read in your device's local time zone, and a date without a time is read as 00:00 UTC. A note under the input names the assumption, so you can add Z or an offset if it is wrong.

What does the Relative line say for dates far away?

It reads just now within about a minute, then minutes, hours and days, with ago or in. Days are the largest unit, so a date years away appears as a large number of days rather than months or years.

Can I convert dates before 1970?

Yes. A negative timestamp is accepted, so -86400 gives 1969-12-31T00:00:00.000Z. In the other direction, any date your browser can parse before the epoch returns a negative number.

Unix Timestamp Converter

Convert Unix timestamps to dates and back.

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About Unix Timestamp Converter

Log lines and API responses often show a moment as a bare number like 1756166400, and it is not obvious whether that counts seconds or milliseconds. Paste it in and the page picks a unit for you: values from 100,000,000,000 upward are read as milliseconds, anything smaller as seconds, and the Unit menu overrides the guess. You get Unix seconds, ISO 8601, UTC, your local time and how long ago or from now it is. Reverse mode parses a date string.

Features

Auto-detects seconds or milliseconds, with a manual Unit override
Shows Unix seconds, ISO 8601, UTC, local time and relative time
Date to timestamp reads ISO 8601 and other formats your browser's Date parser understands
Says which time zone it assumed when the date has none
Rejects impossible ISO dates such as February 31
Accepts negative timestamps for dates before 1970

Limitations

The Unix (seconds) line drops any fraction of a second, although the ISO 8601 line keeps milliseconds.
Local time and the assumed zone come from your device, and there is no menu to pick another time zone.
Date strings that are not ISO 8601 are read by your browser's own parser, so unusual formats can come out differently between browsers.

How it works

Choose Timestamp → Date or Date → Timestamp with the toggle at the top.
Type the number or the date, or select Now to fill in the current time.
In timestamp mode, leave Unit on Auto-detect or switch it to Seconds or Milliseconds.
Read the five results, Unix (seconds), ISO 8601, UTC, Local and Relative, and use Copy beside any of them.

Example input

1756166400

Frequently asked questions

: By size. A ten-digit number such as 1756166400 is below the cutoff and is read as seconds, while a thirteen-digit number is above it and is read as milliseconds. Pick Seconds or Milliseconds in the Unit menu to override the guess.
: A date with a time but no zone is read in your device's local time zone, and a date without a time is read as 00:00 UTC. A note under the input names the assumption, so you can add Z or an offset if it is wrong.
: It reads just now within about a minute, then minutes, hours and days, with ago or in. Days are the largest unit, so a date years away appears as a large number of days rather than months or years.
: Yes. A negative timestamp is accepted, so -86400 gives 1969-12-31T00:00:00.000Z. In the other direction, any date your browser can parse before the epoch returns a negative number.