How to convert Unix timestamps and ISO dates
Seconds versus milliseconds, UTC ISO, and local display — in the browser, without treating a wall-clock zone converter as an epoch parser.
Seconds or milliseconds
Timestamp Converter at /tools/timestamp-converter accepts a Unix number or a parseable date string. Absolute values under 1e12 are treated as seconds and multiplied by 1000; larger values are milliseconds. Output includes unix seconds, unix milliseconds, ISO UTC, and the browser’s local string. Negative epochs (before 1970) are allowed when the engine can represent them. Invalid text is rejected.
Steps
1) Open Timestamp Converter. 2) Paste 1710000000 or an ISO string such as 2024-03-09T16:00:00Z. 3) Read all four fields — local depends on this device’s timezone, ISO UTC does not. 4) Copy the field your API wants. Logs that print milliseconds will not match a seconds field if you mix them.
Not a named-zone converter
Time Zone Converter at /tools/time-zone-converter takes a datetime-local plus IANA names (America/New_York). It answers “what is 3 p.m. in London on this date,” including DST. Timestamp Converter answers “what instant is this epoch.” Date Calculator shifts civil dates by months without Unix. Age Calculator is completed years on a calendar, not an epoch.
Worked example
1710000000 seconds is 2024-03-09T16:00:00.000Z. In a US Pacific browser the local line will not say 16:00. If a JWT exp claim is 1710000000, paste that number here to see the UTC expiry. Do not use this page to schedule cron (Cron Builder) or to count working days (Working Days Calculator).
Common mistakes
Pasting a 13-digit value into a system that expected seconds. Assuming local equals UTC. Parsing “09/03/2024” without knowing month-first vs day-first — prefer ISO. Excel serial dates are not Unix; convert them elsewhere first.
Privacy
Instants stay in the tab. Related: /tools/time-zone-converter, /tools/date-calculator, /tools/cron-builder. Nothing is uploaded.