What is a Unix epoch timestamp?

It is the number of time units that have elapsed since 1970-01-01 00:00:00 UTC, the Unix epoch. Seconds is the classic unit, but APIs often use milliseconds, and high-resolution clocks use microseconds or nanoseconds.

How do the units relate?

Each step up is a factor of 1000: 1 second = 1,000 milliseconds = 1,000,000 microseconds = 1,000,000,000 nanoseconds. The tool multiplies or divides by the right power of 1000 to convert.

Why use BigInt for the math?

Nanosecond timestamps exceed the safe integer limit of JavaScript numbers (about 9 quadrillion), which would lose precision. The tool converts using BigInt so seconds, milliseconds, microseconds, and nanoseconds stay exact.

How is the date calculated?

The value is reduced to milliseconds and passed to the date routines, then formatted in UTC. Sub-millisecond precision (microseconds and nanoseconds) does not affect the displayed calendar time but is preserved in the numeric outputs.

Does it accept negative timestamps?

Yes. Negative values represent instants before 1970-01-01 UTC, so the tool will still convert them and show the corresponding historical UTC date.

Epoch Unit Converter

Convert a single Unix epoch timestamp between seconds, milliseconds, microseconds, and nanoseconds — and instantly see the matching UTC date-time. Useful when one API gives you milliseconds, another wants seconds, and your tracing system logs nanoseconds.

How it works

Every unit is a power of 1000 apart:

1 s = 1,000 ms = 1,000,000 µs = 1,000,000,000 ns

The tool first normalises your input to nanoseconds (the finest unit), then derives every other unit by integer division. Because nanosecond values are far larger than JavaScript’s safe-integer limit, all conversion uses BigInt so no precision is lost:

ns = value * scaleToNs[unit]
seconds      = ns / 1_000_000_000n
milliseconds = ns / 1_000_000n
microseconds = ns / 1_000n

For the human-readable date, the value is reduced to milliseconds and formatted in UTC.

Example

A millisecond timestamp 1780000000000:

Seconds: 1780000000
Microseconds: 1780000000000000
Nanoseconds: 1780000000000000000
UTC date: 2026-05-28 20:26:40 UTC

Notes

Inputs must be whole integers — epoch values do not contain fractional units in these systems. Negative values are valid and represent dates before the 1970 epoch. All math runs locally in your browser with BigInt, so even the largest nanosecond timestamps convert exactly and nothing is uploaded.