Practical example
1700000000 is a timestamp in seconds, while 1700000000000 represents the same instant in milliseconds. A wrong unit shifts the date by millennia.
Timestamp Converter
What is a UNIX timestamp?
A UNIX timestamp is the number of seconds since 1970-01-01 00:00:00 UTC (the Unix epoch). It’s widely used in APIs, logs, databases, and event systems.
Some systems use milliseconds instead of seconds. This tool detects common formats and helps you convert UNIX timestamps to ISO 8601 dates and back — locally in your browser.
How to use the Timestamp Converter
- Paste a UNIX timestamp into the first field (seconds or milliseconds).
- Click “→ ISO” to convert it to an ISO 8601 date (UTC).
- Paste an ISO date into the second field.
- Click “→ UNIX” to convert it back to a UNIX timestamp.
Tips and common pitfalls
- 10 digits usually means seconds; 13 digits usually means milliseconds.
- ISO strings ending with “Z” are in UTC; offsets like +02:00 mean local time zones.
- If your time looks wrong by hours, it’s usually a timezone/offset issue.
- Some systems store timestamps as strings; make sure there are no spaces or commas.
Related guides
Learn the workflow behind this tool and what to check next.
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Timestamp checks before storing or comparing a date
Confirm units, timezone, and precision because the same number can represent different moments when systems make different assumptions.
Seconds or milliseconds
Identify whether the value uses seconds, milliseconds, microseconds, or nanoseconds since the epoch before converting it.
UTC and local time
Store machine timestamps in UTC and apply a named timezone only for display or rules that depend on local civil time.
DST and ambiguity
Test daylight-saving transitions, nonexistent local times, repeated hours, and historical timezone changes.
Precision and range
Check rounding, fractional seconds, negative timestamps, platform range limits, and serialization between languages.
A practical example, an edge case, and a maintainer note
Edge case
A local time during a daylight-saving transition can be missing or occur twice. Convert from an explicit offset or IANA time zone.
Maintainer note
I store instants in UTC and keep the original time zone separately when the user's local calendar time matters.
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Timestamp Converter FAQ
Seconds vs milliseconds — how do I know?
Most UNIX timestamps are 10 digits (seconds). 13 digits typically means milliseconds.
Is the ISO output in UTC?
Yes. ISO strings with “Z” are UTC. If you need a local timezone, convert after you get the ISO value.
Do you store my timestamps?
No. Conversions run in your browser. We don’t store or transmit your input.
Can I convert dates with timezone offsets?
Yes. ISO 8601 can include offsets (e.g., 2026-02-19T12:00:00+02:00). The tool converts it to a UNIX timestamp accordingly.