Unix Timestamp Converter
Unix / POSIX epoch time
Convert machine time and civil time
Result
Calculation summary
Enter values to see the result
Epoch conversion preview
One instant, multiple precisions
How to use this calculator
- 1Choose timestamp-to-date or date-to-timestamp.
- 2Select explicit precision or let digit length detect an entered timestamp.
- 3Choose a display/input IANA zone and convert.
Formula
Unix timestamp = elapsed SI-style units since 1970-01-01T00:00:00Z
BigInt arithmetic preserves whole seconds, milliseconds, microseconds, and nanoseconds before the exact instant is displayed in UTC and a selected zone.
Calculation steps
- Validate the integer timestamp or local date-time.
- Resolve or detect the timestamp precision.
- Scale with integer nanosecond arithmetic.
- Create one exact instant.
- Render UTC, selected-zone, and all four epoch precisions.
Worked example
1,000 Unix seconds is 1970-01-01T00:16:40Z; the equivalent millisecond timestamp is 1,000,000.
Assumptions
- The Unix epoch is 1970-01-01T00:00:00Z.
- Input timestamps are whole integers.
- Automatic detection uses digit length and should be overridden for unusual historic or far-future values.
- POSIX/Unix time does not count leap seconds separately.
- Integer strings are retained to avoid JavaScript Number precision loss.
Sources
Frequently asked questions
Is my timestamp in seconds or milliseconds?
Current timestamps usually have 10 digits in seconds and 13 in milliseconds. Auto uses digit length; choose an explicit unit when known.
Why are large values displayed as text?
Nanosecond and some microsecond values exceed safe floating-point integers, so exact integer strings prevent rounding.
What is the year 2038 warning?
Signed 32-bit systems cannot represent seconds after 2038-01-19T03:14:07Z, though modern systems may use wider values.
Are leap seconds included?
No. POSIX-style timestamps map civil time without counting leap seconds as extra timestamp seconds.
Does time zone change the timestamp?
No. A timestamp is an exact instant; the selected zone changes only its human-readable representation. For date-to-timestamp, the zone defines which instant the wall time means.