What is a microsecond Unix timestamp?

It is the number of microseconds (millionths of a second) since 1970-01-01T00:00:00Z. A present-day value is about 16 digits long and is common in databases like PostgreSQL and in high-resolution logging.

How does this handle large numbers safely?

Microsecond timestamps can exceed JavaScript's safe integer limit, so this tool uses BigInt to split the value into whole milliseconds plus a microsecond remainder, keeping precision exact.

How is it different from milliseconds?

A microsecond value is 1000 times larger than the same instant in milliseconds (about 16 digits versus 13). Divide by 1000 to get milliseconds, or by 1,000,000 to get seconds.

Will I lose the sub-millisecond digits?

No. The tool preserves the microsecond remainder and appends it to the ISO-8601 fractional seconds, so the last three digits are not discarded.

Is my data sent anywhere?

No. Everything is computed locally in your browser using BigInt and the Date API. Nothing is uploaded.

Unix Timestamp (Microseconds) Converter

A Unix timestamp in microseconds counts the number of microseconds (one-millionth of a second) since the epoch 1970-01-01T00:00:00Z. Microsecond resolution appears in databases such as PostgreSQL timestamptz, in tracing systems, and in scientific data. Because these values can be larger than JavaScript can represent exactly with a normal number, this converter uses BigInt to keep every digit correct.

How it works

The tool parses the microsecond value as a BigInt, then splits it into whole milliseconds and a remaining microsecond fraction:

const us = BigInt(input);
const ms = us / 1000n;          // whole milliseconds
const remUs = us % 1000n;       // leftover microseconds (0..999)
const date = new Date(Number(ms));

The Date gives the calendar date-time down to the millisecond, and the leftover remUs is appended to the fractional-seconds part of the ISO-8601 output so no precision is lost. To encode, the tool parses the date to milliseconds and multiplies by 1000n.

A present-day microsecond timestamp is about 16 digits, for example 1700000000000000. If your value has ~13 digits it is in milliseconds; ~10 digits means seconds.

Tips and notes

BigInt is used so timestamps past Number.MAX_SAFE_INTEGER (about 9 quadrillion) stay exact.
Date-time parsing only resolves to millisecond precision, so encoding a string yields a microsecond value ending in three zeros unless the string itself carries microsecond digits.
Always store the canonical UTC form; local time is for display only.