A Chrome / WebKit timestamp value counts microseconds from 1601-01-01T00:00:00Z. Its source epoch and unit need to travel with it; the number alone cannot tell you which clock it belongs to.

Conversion rule

Unix milliseconds = WebKit microseconds / 1000 − 11644473600000

The converter applies that relationship and returns Unix seconds, epoch milliseconds, ISO 8601 UTC, and a readable UTC value. Keep the original value as well when investigating a log or export so the conversion can be checked later.

Where mistakes happen

This format shares the 1601 epoch with Windows FILETIME but uses microseconds rather than 100-nanosecond intervals.

A safer workflow

  • Identify the platform and field name before doing arithmetic.
  • Preserve the original value as a string when it may exceed JavaScript safe-integer precision.
  • Convert once at the boundary, then store or compare a declared Unix unit.
  • Format in a named timezone only when presenting the resulting instant to a person.
FILETIME.NET TicksExcel OADateNTPUnix Epoch Converter

Frequent questions:

Q: What epoch does Chrome use for timestamps?
A: Chromium/WebKit timestamps count microseconds since January 1, 1601 00:00:00 UTC — the same epoch as Windows FILETIME, but in microseconds rather than 100-nanosecond ticks.
Q: How do I convert a Chrome history timestamp?
A: Divide the value by 1,000,000 and subtract 11,644,473,600 to get a Unix timestamp in seconds, then format it as a date.
Q: Why is the Chrome timestamp 17 digits?
A: Because it counts microseconds (a millionth of a second) since 1601, accumulating over 400 years of microseconds produces a 17-digit number.