Timestamp Converter
Convert Unix timestamps (s/ms) to dates and back. Shows UTC and local time together.
About this tool
A Unix timestamp represents time as the number of seconds elapsed since 00:00:00 on January 1, 1970 in Coordinated Universal Time (UTC). Because it is a single number independent of time zone, it serves as a common language for passing times between systems. This tool converts between numbers and dates in your browser and never sends your input anywhere.
Seconds vs milliseconds (digit count)
The same "now" is about 10 digits in seconds but about 13 digits in milliseconds. JavaScript works in milliseconds internally, while UNIX commands and databases often use seconds; mixing them up shifts the value by 1000x and lands you in "1970" or the far future. Use the digit count as a cue to confirm the unit.
The Year 2038 problem
Older systems that store the timestamp in a signed 32-bit integer overflow just after 03:14:07 UTC on January 19, 2038, corrupting the time. This is the "Year 2038 problem". Storing it in 64 bits is now standard, and this tool handles values without overflow concerns, but it is worth keeping in mind when touching old implementations like C's time_t.
Leap seconds are not counted
Unix time is computed with a fixed "1 day = 86400 seconds" and does not count the leap seconds occasionally inserted into real UTC. So strictly speaking its definition differs slightly from UTC, but for everyday logs and API exchanges you can treat them as matching in practice.
Store in UTC, display in local
The convention is to store time as a timestamp (a UTC-based number) and convert to the viewer's time zone only for display. To keep a human-readable form, an ISO 8601 string like 2024-01-01T09:00:00+09:00 leaves the least room for misreading, and this tool can produce ISO 8601 output too.
How to use
- Use "Timestamp β Date" to turn Unix seconds/ms into a date.
- Use "Date β Timestamp" to turn an ISO date string into Unix values.
- Press Now to grab the current timestamp.
FAQ
How are seconds and milliseconds distinguished?
The unit is detected automatically from the number of digits. Roughly, large values of about 13 digits or more are treated as milliseconds and smaller values as seconds, then converted to a date.
What is a Unix timestamp?
A way of representing time as the elapsed time since 00:00:00 on January 1, 1970 in UTC. Because it is an absolute value independent of time zone, it is widely used for exchanging times between systems.
Can I see both UTC and local time?
Yes. The result is shown in both UTC and your device's local time, which prevents mix-ups caused by environment differences.
Can I get a Unix timestamp from a date?
Yes. Enter a date and time to get the corresponding Unix timestamp in seconds and milliseconds. Conversion works both ways.
Are the values I enter sent to a server?
No. Conversion happens entirely in your browser, and the values you enter are never sent externally.
I want to check the time in a different time zone.
The local time display is based on your device settings. To check a specific other time zone, pairing this with a time zone converter makes it clearer.