Unix Timestamp Converter
Convert a Unix timestamp in seconds or milliseconds, or an ISO 8601 date and time, to UTC.
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How to use this
Choose the input unit, enter the value, then convert. Read the UTC date and both timestamp units.
Seconds allow up to 3 decimal places with a dot; milliseconds must be integers. Date/time input needs Z or an offset.
Example input
1709164800 s
Expected result
2024-02-29T00:00:00.000Z · 1709164800000 ms
1709164800 seconds and 1709164800000 milliseconds represent 2024-02-29 at 00:00 UTC.
More detail
An ISO date without a time means midnight UTC. The browser limits the supported date range.
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Quick answer
Convert Unix seconds, Unix milliseconds, or an ISO date or date/time to UTC. The result also shows the matching value in both timestamp units.
The page and its assets load from the site; this operation uses your entered values only in this browser and does not send them to a calculation endpoint.
How to use it
Choose Unix seconds, Unix milliseconds, or an ISO 8601 date or date/time. Seconds accept up to three decimal places; milliseconds must be whole numbers. A date-only ISO value is read as midnight UTC. A date/time must include Z or an offset such as +02:00. The result shows UTC and both timestamp units.
Limits
Seconds may include up to three decimal places (millisecond precision); milliseconds must be whole numbers. ISO date-only input means midnight UTC, while date/time input must include Z or a UTC offset. Results are limited to the date range supported by the browser.
Frequently asked questions
What does a Unix timestamp measure?
It counts time from 1970-01-01 00:00:00 UTC. Choose seconds or milliseconds to match the unit of the number you have.
How precise can the input be?
Seconds may have up to three decimal places, which represent milliseconds. Millisecond input must be a whole number; the browser Date value has millisecond precision.
How are ISO dates interpreted?
A date without a time is treated as midnight UTC. A date/time must include Z or a numeric UTC offset, such as +02:00; the result is always shown in UTC.
Why is my ISO date/time rejected?
The calendar date must exist, and the clock fields and UTC offset must be valid. These input errors are different from a numeric timestamp that falls outside the browser’s supported date range.
Sources and references
These references document the cited standard or browser API; they do not validate the tool’s output.