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Timestamp Converter

Convert Unix timestamps to ISO, UTC and local time (and back) in your browser. Seconds and milliseconds are auto-detected, with the guess explained.

Timestamp → date

Date → timestamp

Uses your browser’s local timezone for the input.

Your file is never sent to a server. It is read and processed by your own browser, and the results are not stored.

How to use it

  1. Paste a Unix timestamp (seconds or milliseconds).
  2. Read ISO, UTC, local and relative renderings side by side.
  3. Or fill in the date/time fields and get the epoch value in seconds and milliseconds.

Limits worth knowing

  • Automatic mode assumes ≥ 1e11 is milliseconds; force a unit when you know better.
  • Dates are limited to what JavaScript Date can represent (about 8.64 × 10^15 ms from the epoch).
  • Leap seconds are not modelled — Unix time counts them as ordinary seconds.
  • Local display uses your browser’s timezone and locale.

Seconds vs milliseconds, settled

Unix time counts seconds from 1970-01-01T00:00:00Z. JavaScript counts milliseconds. The same instant is 1778008000 in one and 1778008000000 in the other — a factor of a thousand that has caused more off-by-1970 bugs than any other in computing. Automatic mode guesses; the readout always shows which unit it applied.

If you are debugging a log line, compare the ISO output with what the system claimed. A mismatch means seconds were read as milliseconds, or vice versa.

Relative time is relative to your clock

The relative phrase compares against Date.now() in your browser, rounded and honest — “3 days ago”, not “in 72 hours, probably”. If your clock is skewed, so is the phrase.

Frequently asked questions

Does Timestamp Converter upload my files to any server?

No. Timestamp Converter runs in your browser, and the file is read there rather than sent to a server for processing. Our host still sees ordinary page-request metadata, which is described on the privacy page.

Is Timestamp Converter free to use?

Yes, Timestamp Converter is free, with no paid tier, no account, and no watermark added to your output. The limits are technical rather than commercial: file size, page count and supported formats are listed on this page.

What file formats and sizes are supported?

Timestamp Converter supports .txt files up to 1MB directly in your browser.

Is my input seconds or milliseconds?

In automatic mode, anything ≥ 1e11 is treated as milliseconds and anything smaller as seconds. Around that boundary you can switch the unit explicitly — the tool shows which interpretation it used.

Why does 1778008000 look like a date in 2026?

That is exactly what it is: 2026-05-05 UTC. A 10-digit timestamp is seconds; a 13-digit one is milliseconds. Mixing the two gives dates in 1970 or in the distant future, which is the bug this tool exists to spot.

What happens with out-of-range timestamps?

You get an error, not a silently wrapped date. JavaScript Date cannot represent times beyond about ±8.64 × 10^15 ms.

Does it use my computer’s timezone?

The local display uses your browser’s timezone. The ISO and UTC outputs are always UTC, so log lines paste identically everywhere.