Unix Timestamp Converter

How it works

The epoch is 1970-01-01 at midnight UTC. Multiply seconds by 1,000,000,000 to obtain nanoseconds; milliseconds by 1,000,000; microseconds by 1,000. BigInt preserves integer precision. Coarser epoch units floor toward negative infinity. UTC retains nine fractional digits; local and IANA displays use the browser date facilities and do not show submillisecond precision. Leap seconds are excluded.

Auto mode guesses seconds for up to 10 magnitude digits, milliseconds up to 13, microseconds up to 16 and nanoseconds thereafter. This is a heuristic for recent dates, not a standard; choose an explicit unit for small or distant timestamps. Signed six-digit expanded years are accepted except -000000. Hour 24 is accepted only with zero minutes, seconds and fraction, meaning midnight at the end of that day. Reverse conversion requires an explicit Z or UTC offset, avoiding ambiguous daylight-saving wall times. IANA zones affect display only. Batches allow 10,000 lines and 1 MiB; errors clear the whole batch.

Worked examples

Unix epoch

0 seconds gives 1970-01-01T00:00:00.000000000Z and 0 nanoseconds.

One nanosecond before the epoch

-1 nanosecond gives 1969-12-31T23:59:59.999999999Z. Floored epoch seconds are -1.

Frequently asked questions

Sources

• W3C Long Tasks API — discontinued draft, task responsiveness (checked 2026-11-14)
• ECMA-262 — Date time values and date string format (checked 2026-11-14)
• Linux man-pages — time(2) (checked 2026-11-14)