What this tool does
Convert Unix timestamps (seconds / milliseconds) to ISO 8601 and back, with multi-timezone display, in your browser.
No network calls are needed; everything runs locally.
How to use
- Enter a timestamp or ISO string Pure digits are treated as a timestamp; anything with letters, "T" or "Z" is treated as an ISO string.
- Pick a unit and a timezone Auto-detect is the default (≤10 digits → seconds, otherwise → milliseconds); the timezone is used for the formatted display.
- Copy or download the result The output includes Unix seconds, Unix milliseconds, UTC ISO, local ISO and the target-timezone string.
FAQ
How do you tell seconds from milliseconds?
By length: ≤10 digits (absolute value) is usually seconds, 13 digits is usually milliseconds. Seconds timestamps stay 10 digits wide for decades, so this rule is stable; if you need certainty, pick the unit manually.
What about the year-2038 problem?
It only affects 32-bit signed second columns. Internally this tool uses 64-bit floats (JS Number) and is good for ~285 million years. The real risk is in databases that store seconds in INT columns — those must move to BIGINT or to milliseconds.
Why do you not expand timezone abbreviations like CST or PST?
CST has at least four meanings (China Standard, US Central Standard, Cuba Standard, Central Standard); abbreviations are too ambiguous. This tool only accepts full IANA names like Asia/Shanghai or America/New_York.
Is anything uploaded?
No. Parsing happens inside your browser; the server only serves the page.
Can I do date arithmetic?
This tool does not do arithmetic like "add N days" or "subtract N hours". Add 86400 to the Unix seconds yourself and convert back here, or use a dedicated date-arithmetic tool.
Limits
Seconds/millisecond conversion and multi-timezone display only — no date arithmetic, no cron parsing, no custom timezone abbreviations.
Timezone math relies on the browser tzdata; minimal browsers without tzdata fall back to UTC.