Unix Timestamp Converter
Convert between Unix timestamp and ISO 8601. Seconds and milliseconds are detected automatically.
This tool runs in your browser. No data leaves your device.
- UTC
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- Local
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- RFC 2822
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- Relative
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- Epoch (s)
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- Epoch (ms)
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How It Works
A Unix timestamp is the number of seconds elapsed since 1 January 1970 UTC. This tool detects both seconds and milliseconds input automatically (large numbers are interpreted as ms).
Seconds or milliseconds?
- PHP
time()— seconds. - Python
time.time()— seconds (with a fractional part). - JavaScript
Date.now()— milliseconds. (This difference is the most common source of bugs when you try to make JavaScript talk to other languages.) - PostgreSQL
extract(epoch from now())— seconds (with a fractional part). - Redis
TIMEcommand — seconds + microseconds.
When you design an API, write the unit decision into the documentation. Otherwise clients forget to multiply/divide by 1000 and you end up with “your dates are in 1970” bugs.
UTC vs local
A Unix timestamp is always UTC. When local time is shown, your browser’s time zone has been applied.
In production, keep server logs in UTC. Converting on the client side is always cleaner than drifting into timezone confusion on the server.
ISO 8601
The 2026-05-18T14:30:00.000Z format is a specific variant of ISO 8601 — the trailing
Z means “Zulu time”, i.e. UTC. This format:
- Sorts correctly in date order (as a string).
- Is accepted by all modern APIs and databases.
- Carries no ambiguity (the time zone is always specified).
Always send date fields in your APIs as ISO 8601.
The year 2038 problem
A Unix timestamp stored as a 32-bit signed integer overflows on 19 January 2038. Newer systems use 64-bit and never hit this problem. For old C code or embedded systems, it’s still a risk.
Privacy
All conversions run entirely in your browser.