Convert Unix Timestamps and Time Zones

A Unix timestamp describes an instant relative to 1970-01-01 00:00 UTC. The same instant can be written in different units and shown on different local clocks.

Work through the task

1. Select the known timestamp unit. Do not rely on digit count to guess whether a source uses seconds or milliseconds.
2. Convert to UTC first, then choose a supported IANA display zone. This changes the displayed clock, not the instant.
3. For reverse conversion, enter a date, clock time and zone. Here changing the zone keeps the typed wall clock and can change the instant.
4. If that clock time repeats, select the first or second occurrence using the displayed offsets. Correct a skipped time yourself.

Checked examples

Calculation method

The converter scales strict decimal values to integer nanoseconds and uses Temporal for instant/calendar conversion. Decimal unit output preserves the same nanosecond count. Zone conversion and calendar-date subtraction are different operations.

Assumptions and limits

Unix time here ignores leap seconds and second 60 is rejected. The device supplies current time and the browser supplies time-zone rules. Supported UTC and local years are 0001–9999. No network clock, automatic timestamp detection or URL sharing of entered values is used.