Understand this tool
Convert Unix time without guessing the unit
- What the concept means
- Unix time counts elapsed seconds from 1970-01-01 00:00:00 UTC, called the Unix epoch.
- Why it exists
- It gives software a compact numeric time coordinate that is independent of local calendar display.
- When to use it
- Use it to convert known seconds or milliseconds and inspect interoperable system timestamps.
- What the result means—and does not mean
- A timestamp denotes an instant only when its unit is known. It contains no time-zone label and ordinary Unix time does not represent leap seconds as distinct counted seconds.
Epoch, units, and the 2038 problem
The epoch is a conventional origin, not the beginning of computing. Systems use seconds, milliseconds, microseconds, or nanoseconds, so the same digits can describe radically different dates if interpreted in the wrong unit.
A signed 32-bit seconds counter reaches its maximum in January 2038. Modern systems commonly use wider representations, but older storage formats, embedded systems, and protocols may still be affected.
UTC and leap seconds
Unix timestamps are commonly converted through UTC for display, then localized to a time zone. POSIX-style Unix time generally maps days as 86,400 seconds and does not assign a unique number to an inserted leap second, so it is not a perfect count of every SI second.
Key concepts
Key concepts
- Unix time
- A numeric time scale counted from the Unix epoch.
- Unix epoch
- 1970-01-01 00:00:00 UTC.
- UTC
- The civil time standard used as the conversion reference.
- Timestamp unit
- Seconds, milliseconds, microseconds, or nanoseconds per count.
- Year 2038 problem
- Overflow of signed 32-bit Unix seconds.
- Leap second
- An occasional UTC adjustment not uniquely represented by ordinary Unix time.
Method or process
How the process works
UTC and leap seconds
Unix timestamps are commonly converted through UTC for display, then localized to a time zone. POSIX-style Unix time generally maps days as 86,400 seconds and does not assign a unique number to an inserted leap second, so it is not a perfect count of every SI second.
Compare the concepts
Common timestamp units
| Unit | Counts per second | Typical digit length today |
|---|---|---|
| Seconds | 1 | 10 |
| Milliseconds | 1,000 | 13 |
| Microseconds | 1,000,000 | 16 |
Common mistakes
Common mistakes
- Confusing seconds with milliseconds.
- Reading the number as a local time zone.
- Assuming Unix time uniquely counts leap seconds.
Edge cases and limits
Edge cases and limits
- Negative values represent instants before the epoch.
- Very large values can exceed JavaScript Date range or precision.