Unix Timestamp Converter

How to use

1. Paste an integer into “Unix timestamp”; the converted seconds, milliseconds, ISO 8601, and readable time appear immediately.
2. Leave Input unit on “Auto” for ordinary 10-digit seconds and 13-digit milliseconds, or select the known unit to override that convention.
3. To convert in the other direction, edit “Date and time” and choose whether that clock time means UTC or your device’s local time.
4. Use “Use current time” to start from the current instant, then copy an individual value or all values together.
5. Your last inputs stay only in this browser; press / outside a field to focus the timestamp input again.

Unix time is an instant, not a time zone

A Unix timestamp is a count from 1970-01-01 00:00:00 UTC, commonly called the Unix epoch. The same integer names the same instant everywhere; a time zone only changes the human-readable clock used to display it. This tool therefore keeps ISO 8601 in UTC and lets you explicitly read a date/time entry as either UTC or this device’s local zone. That distinction matters for strings without an offset: “2024-01-01 09:00” means a different instant in Seoul and New York, while “2024-01-01T00:00:00Z” always means UTC.

Seconds, milliseconds, and the safe way to detect them

Unix and POSIX tools usually use whole seconds, so current values are 10 digits; JavaScript Date.now() returns milliseconds, which are currently 13 digits. Auto mode follows that common convention: up to 10 significant digits are read as seconds and longer integers as milliseconds. Digit count is a useful hint rather than a permanent specification—Unix seconds become 11 digits in 2286—so this converter always shows the detected unit and provides a manual override. It also preserves the millisecond remainder exactly: 1704067200123 milliseconds is shown as 1704067200.123 seconds, not a rounded floating-point value.

Range and leap-second limits

The browser Date object used here can represent instants from roughly 275,760 years before to 275,760 years after 1970, and the converter rejects values outside that range instead of silently rounding them. Unix time does not count leap seconds: its scale proceeds as though each UTC day has 86,400 seconds. That is why it is excellent for ordering logs, API events, expiry times, and database values, but it is not a record of every atomic-clock second. For timestamps with microseconds or nanoseconds, retain the original value in the source system because JavaScript Date displays millisecond precision.

Frequently asked questions