The Complete Unix Timestamp Guide: Seconds, Milliseconds & Dates
A Unix timestamp is the number of seconds since 1970-01-01, used by almost every system to record time. Understand it and time-zone and log issues become easy.
Seconds or milliseconds
Many systems use seconds (10 digits), while JavaScript's Date.now() returns milliseconds (13 digits). 1000× apart — confusing them shows the time as 1970.
UTC vs local time
- UTC is Coordinated Universal Time, independent of time zone
- Local time = UTC ± zone offset
- Store in UTC, convert only when displaying
Convert online
FreeToolset's timestamp tool converts seconds/milliseconds both ways and shows UTC and local time for easy checking.
💡 When log times don't match, first confirm seconds vs milliseconds, then check the time-zone setting.