Free Unix / Epoch Timestamp Converter

How this tool computes its result

Provides bidirectional conversion between Unix timestamps and human-readable dates. The timestamp-to-date path parses numeric input (detecting whether the number is in seconds or milliseconds by checking if its absolute value is ≥10¹²), then constructs a Date object from the milliseconds value, converts to both UTC and local time strings, and extracts seconds and milliseconds separately for display. The date-to-timestamp path takes a datetime-local input (which is already timezone-agnostic), constructs a Date object, and outputs both seconds and milliseconds representations. Both paths include ISO 8601 (UTC) and locale-specific string representations.

Worked example

Entering epoch value "1710139200" (in seconds, less than 10¹²) converts to a Date representing March 11, 2024 at 16:00:00 UTC. The tool outputs seconds as 1710139200, milliseconds as 1710139200000, and ISO format as "2024-03-11T16:00:00.000Z". Conversely, picking the date March 11, 2024 at 4:00 PM in the datetime-local picker produces seconds as 1710141600 (shifted by local timezone offset) and milliseconds as 1710141600000.

When not to use this tool

The auto-detection of seconds vs milliseconds has a boundary at 10¹² — timestamps between year 2001 and year 33658 in milliseconds can be misinterpreted as seconds. Also, the datetime-local input picker returns times in the browser's local timezone but the picker UI has no explicit timezone indicator, so users working across time zones may unwittingly enter times in the wrong reference frame.

Common mistakes

• - Entering a timestamp in the wrong unit (seconds vs milliseconds) and not double-checking the output — if you paste a 13-digit timestamp (milliseconds) but the tool interprets it as seconds, the resulting date will be roughly 1000x in the future.
• - Expecting UTC and local time representations to refer to the same instant — they do, but if you enter a datetime-local time and then convert it back to an epoch, the seconds value will differ by your timezone offset.
• - Using the ISO output directly as a filename or log key assuming it's timezone-aware — the ISO string includes "Z" indicating UTC, but the UTC time shown is the browser's current timezone view of the input, not necessarily the time the user intended if they didn't account for DST or UTC offset.

Related tools