What it does

Enter a Unix timestamp or an ISO-8601 date and read the same instant back in every common form. When you enter a number, the tool auto-detects its unit (seconds, milliseconds, microseconds, or nanoseconds) from its magnitude, so you can paste a value from almost any system without saying which unit it is. It then renders the instant as a UTC calendar breakdown, an ISO-8601 string, an RFC 3339 timestamp, the HTTP date format, and the timestamp itself in all four units. Everything is computed in your browser.

What Unix time means

Unix time, defined by POSIX, is the number of seconds elapsed since the epoch (1970-01-01 00:00:00 UTC), not counting leap seconds. Different systems store it at different resolutions: classic Unix and most APIs use seconds; JavaScript and many databases use milliseconds; some tracing and kernel interfaces use microseconds or nanoseconds. Because those magnitudes are roughly a thousand apart, the unit can be inferred from how many digits the number has, which is what the auto-detection does.

The formats it produces

  • UTC calendar breakdown, the year, month, day, and time of day in UTC.
  • ISO 8601 and RFC 3339, the internet timestamp format, for example 2026-07-01T20:00:00Z.
  • HTTP date, the IMF-fixdate form used in HTTP headers (RFC 9110, section 5.6.7), for example Wed, 01 Jul 2026 20:00:00 GMT.
  • All four units, the same instant expressed as seconds, milliseconds, microseconds, and nanoseconds.

Range and determinism

Dates are handled within the range a JavaScript date value can represent, roughly plus or minus 273,000 years around the epoch (a limit of 8.64 x 10^15 milliseconds on either side). The conversion is a pure function of the input value and never reads the current clock, so a given timestamp always renders the same way. A "relative to now" convenience necessarily needs the wall clock, so it lives in the tool's interface rather than in this deterministic core.

Using it

Enter a Unix timestamp such as 1751400000 (a ten-digit value, so it is read as seconds) or 1751400000000 (thirteen digits, read as milliseconds), or an ISO-8601 date such as 2026-07-01T20:00:00Z, and read every equivalent form at once.