Timestamp / Epoch Converter
Epoch → ISO 8601
ISO 8601 → Epoch
Cmd/Ctrl+Enter saves the current value to history.
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Convert a Unix epoch value to an ISO 8601 date, or the reverse. Epoch input can be seconds or milliseconds — pick explicitly rather than relying on digit-count guessing, since both are common depending on the API or language that produced the number (JavaScript's Date.now() gives milliseconds; most Unix tools give seconds).
Frequently asked questions
- How do I know if my timestamp is in seconds or milliseconds?
- Seconds since 1970 are 10 digits today (e.g. 1735689600); milliseconds are 13 digits (e.g. 1735689600000). This tool has an explicit seconds/milliseconds switch instead of guessing from digit count, since a guess is exactly the kind of thing that silently produces a date 50,000 years off.
- Why does converting my timestamp give an error?
- Two ways this fails: the input isn't a valid number at all, or it's a number but produces an out-of-range date (JavaScript's Date can't represent it). Non-numeric input — stray text, a copied cell reference — is the most common cause.
- What timezone is the converted date shown in?
- The ISO 8601 output is UTC (the Z suffix) — Unix time itself has no timezone, it's a count of seconds/milliseconds since the epoch. Convert to a local timezone in whatever consumes the output, not here.
- Is my data uploaded anywhere?
- No. Conversion happens locally in your browser tab — nothing is sent to a server.
Read the full guide for this tool →
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