Unix Timestamp to Date
Convert a Unix timestamp into an ISO 8601 UTC date and time. Enter either a conventional ten-digit seconds value or a longer milliseconds value; the tool infers the unit from digit length. Conversion runs locally and returns an ISO string ending in Z.
Runs locally — files stay on your deviceWhat does a Unix timestamp represent?
It counts elapsed seconds, or sometimes milliseconds in browser systems, from 1970-01-01 00:00:00 UTC.
Unix time counts from an epoch
Unix time represents elapsed time since 1970-01-01 00:00:00 UTC, traditionally in seconds. JavaScript Date uses milliseconds internally, so seconds values must be multiplied by one thousand.
How it works
The implementation parses a finite number, treats values of ten digits or fewer as seconds and longer values as milliseconds, constructs a Date, and emits toISOString in UTC.
When to use it
- Read timestamps from logs.
- Translate an API epoch value.
- Compare seconds and milliseconds representations.
When not to use it
- Do not assume the output uses local time.
- Do not rely on digit inference for unusual historical or far-future values.
- Do not use it to infer a user's time zone.
Worked examples
Unix epoch
- Input
0- Expected output
1970-01-01T00:00:00.000Z
Zero is the epoch instant.
Seconds value
- Input
1704067200- Expected output
2024-01-01T00:00:00.000Z
Ten digits are interpreted as seconds.
Milliseconds value
- Input
1704067200000- Expected output
2024-01-01T00:00:00.000Z
Thirteen digits match JavaScript milliseconds.
Common mistakes
Mixing seconds and milliseconds
A factor-of-1000 error creates a very different date. Correction: Check the source API's unit.
Reading Z as local time
Z denotes UTC. Correction: Convert separately for local display.
Assuming epoch values contain a timezone
They represent an instant, not a named zone. Correction: Apply the desired zone when formatting.
Related operations and differences
Date to Unix Timestamp
It performs the reverse conversion from a selected date and time.
Limitations and privacy
- Unit detection is based on digit length.
- JavaScript Date range and precision limits apply.
Processing uses browser APIs on this device; the entered content is not sent to the Toolbox server.
Frequently asked questions
Are Unix timestamps seconds or milliseconds?
Unix convention uses seconds; many browser APIs use milliseconds. This tool infers common forms.
What does the trailing Z mean?
It identifies UTC.
Does a timestamp store a timezone?
No. It represents an instant relative to UTC.
Why is my date near 1970?
A milliseconds value may have been interpreted as seconds or vice versa.