Unix Timestamp Converter — Seconds, Milliseconds & ISO

How it works

Choose seconds or milliseconds explicitly; the tool does not guess from the number of digits. Enter an integer timestamp to see UTC ISO output and a localized view in the selected timezone. The reverse conversion accepts a four-digit ISO year and a time with Z or an explicit offset. This avoids interpreting an unzoned time differently on another computer.

Limits and behavior

Invalid dates such as February 30 and times such as 24:00 are rejected rather than normalized. ISO fractions support up to three decimal places. Leap seconds are not supported. Milliseconds are exact within the supported JavaScript date range; displayed Unix seconds are floored, including before 1970. Named-zone display uses your browser’s timezone database.

Example

Unix 0 seconds is 1970-01-01T00:00:00.000Z. The ISO date 1970-01-01T07:00:00+07:00 represents the same instant. A value of −1 millisecond corresponds to Unix second −1 when floored.

Assumptions and limitations

Start with Load example to see the expected input shape. Replace the example with your own text and choose the relevant operation. Editing an input invalidates the previous output so an old result cannot be copied as if it were current. Copy and download buttons become available after a successful run. Clear removes the visible inputs and output from the page. Limits keep small development tasks responsive; use a local editor or dedicated command-line utility for very large files. A successful transformation does not validate your application logic or make untrusted data safe to execute.

Sources

MDN Web Docs

Frequently asked questions