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Unix Timestamp Converter

Epoch seconds to a readable date, and back again.

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Detect distinguishes seconds from milliseconds by magnitude.

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A Unix timestamp counts seconds since 1 January 1970 UTC. 1700000000 is 14 November 2023 at 22:13 UTC. Ten digits means seconds, thirteen means milliseconds.

How to use Unix Timestamp Converter

  1. Paste your values. Timestamps or dates, one per line — you can mix both.
  2. Let it detect the unit. Ten-digit numbers are read as seconds, thirteen-digit as milliseconds.
  3. Read every format. Human-readable, ISO 8601, seconds and milliseconds together.

About converting Unix timestamps

A Unix timestamp is a single number counting seconds since midnight UTC on 1 January 1970. Its appeal is that it is unambiguous in a way a written date is not: no time zone, no locale, no argument about whether 03/04 is March or April. Storing an instant as one integer removes an entire category of bug, which is why almost every system does it. The confusion that remains is about units. JavaScript, Java and several databases count in milliseconds while C, Python and most Unix tooling count in seconds, and the two are a factor of a thousand apart. The failure is distinctive and easy to recognise once you have seen it: pass milliseconds to something expecting seconds and you get a date tens of thousands of years in the future, while passing seconds where milliseconds are expected lands you in January 1970. Length is the practical tell — ten digits for seconds through this century, thirteen for milliseconds. Two limits are worth knowing. Systems storing the value in a signed 32-bit integer overflow on 19 January 2038 and wrap to 1901; anything modern uses 64 bits, but embedded firmware and older file formats still carry the constraint. And Unix time deliberately ignores leap seconds, treating every day as exactly 86,400 seconds, which means it is not a true count of elapsed time. For everything short of scientific timing that is the right trade, because the alternative is arithmetic that requires a table of historical adjustments.

Frequently asked questions

What is the Unix epoch?
Midnight UTC on 1 January 1970, the zero point almost all computing time is measured from. It was chosen for practical reasons at Bell Labs rather than any significance in the date itself, and it stuck because everything built afterwards assumed it.
How do I tell seconds from milliseconds?
By length. A seconds timestamp for any date between 2001 and 2286 is ten digits; the same instant in milliseconds is thirteen. If a date comes out in 1970, you have almost certainly passed milliseconds to something expecting seconds.
What is the year 2038 problem?
A signed 32-bit integer overflows on 19 January 2038, at which point systems still storing timestamps that way will wrap to 1901. Modern systems use 64-bit values and are unaffected, but embedded devices and old file formats still carry the limit.
Do Unix timestamps handle leap seconds?
No, and deliberately. Unix time treats every day as exactly 86,400 seconds, so a leap second is not represented — the count either repeats a value or is smeared across several hours, depending on the system. It means Unix time is not a true count of elapsed seconds, which rarely matters outside precise scientific work.
Why is everything shown in UTC?
Because a timestamp has no time zone — it is an absolute instant, and the zone is a presentation choice made when displaying it. Showing UTC avoids implying the number carries an offset it does not have.

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