Unix Timestamp Converter

How the tool decides between seconds and milliseconds

The rule counts digits: a whole number with 13 or more digits is read as milliseconds, and a whole number with up to 12 digits is read as seconds and multiplied by 1,000. Both 1750000000 (ten digits) and 1750000000000 (thirteen digits) therefore land on the same instant, Sunday 15 June 2025 at 15:06:40 UTC, and the note above the results tells you which unit was assumed.

A decimal point marks a seconds value with a fraction: 1750000000.5 is read as seconds, and the half second shows up in the ISO line as 2025-06-15T15:06:40.500Z. A plain 12-digit number such as 100000000000 stays seconds, which puts it in the year 5138, so a millisecond value must carry its full thirteen digits. Negative numbers work and go back before 1970: -1 is 31 December 1969 at 23:59:59 UTC, and the minus sign is not counted as a digit.

The three output formats explained

Because the local line depends on your device settings, two people pasting the same number can see different wall-clock times while the UTC and ISO lines stay identical. There is no zone selector, so to see the time in another zone use the ISO value with a time zone converter.

Date to timestamp: which zone the picker uses

The date picker is a plain datetime-local field, which has no zone of its own. The browser interprets what you choose in your device's current zone and the tool divides the resulting milliseconds by 1,000, rounding down. Choosing 15 June 2025 at 15:06 on a computer set to London (British Summer Time, UTC+1) gives 1749996360, while the same choice in New York (UTC−4) gives 1750014360, a difference of five hours. If you need the timestamp of a UTC wall-clock time, shift the time you enter by your own offset, or temporarily change the computer's zone.

Most browsers let the picker select minutes only, so the seconds value usually ends in a multiple of 60 and the millisecond value ends in 000.

Landmark values worth recognising

Spotting the unit in the wild

• Ten digits means seconds, which is what JWT exp and iat claims, Python's time.time() (as a float), PHP's time() and most REST APIs use.
• Thirteen digits means milliseconds, as produced by JavaScript's Date.now() and Java's System.currentTimeMillis().
• Sixteen digits are microseconds and nineteen digits are nanoseconds (Go, Kafka, some database drivers). The tool treats both as milliseconds, which yields a date tens of thousands of years away or an out-of-range error, so divide by 1,000 or 1,000,000 first.
• Unix time ignores leap seconds: every day is exactly 86,400 seconds, so the count is a few dozen seconds short of a strict atomic count since 1970.

When a red message appears instead of a date

If the box contains anything that is not a plain number, including commas, units, exponent notation or an ISO date, a red line under the box lists the three shapes it accepts: seconds with up to 12 digits, milliseconds with 13 or more, or seconds with a decimal fraction. A second message covers numbers that parse but fall outside the range a JavaScript Date can represent, about 8.64 × 10^15 milliseconds either side of 1970, roughly 275,000 years; it repeats which unit the value was read as, so a nanosecond timestamp is easy to recognise. Strip any formatting and make sure the number is in seconds or milliseconds.