Published 2026-04-05

Unix Timestamp Converter Guide: Seconds, Milliseconds, and Time Zones

Understand Unix timestamps, common conversion mistakes, and how to avoid timezone bugs.

Unix timestamps represent the number of seconds that have elapsed since January 1, 1970 UTC. Some systems store milliseconds instead of seconds, which is one of the most common causes of bugs.

If your timestamp has 13 digits, it is usually milliseconds. If it has 10 digits, it is usually seconds.

Always verify whether timestamps are interpreted in UTC or converted to a local timezone in the UI. Many date bugs are actually timezone bugs.

A converter should support both directions: timestamp to human-readable date and date to timestamp.