Unix Milliseconds Converter
Convert between Unix epoch milliseconds and a calendar date/time in UTC, with full millisecond precision.
Direction
ms
Milliseconds since the Unix epoch (1970-01-01 00:00:00 UTC)
How does this calculator work?
Unix milliseconds are the number of thousandths of a second since 1970-01-01 00:00:00 UTC. Enter a millisecond value to get its ISO 8601 date and time, or enter a UTC date and time to get the millisecond timestamp. Equivalent Unix seconds equal milliseconds divided by 1000.
Formula
How this is calculated
Unix time counts the elapsed time since the epoch, 1970-01-01 00:00:00 UTC. While classic Unix timestamps use whole seconds, JavaScript and many APIs use milliseconds, so this tool works in milliseconds and shows the equivalent seconds (milliseconds / 1000) alongside the millisecond-within-second remainder (milliseconds mod 1000).
In "Milliseconds to date" mode, the entered millisecond value is passed to new Date(ms), and the result is reported as an ISO 8601 string plus separate UTC date and UTC time fields. In "Date to milliseconds" mode, the UTC date (YYYY-MM-DD) and the hour, minute, and second inputs are combined with Date.UTC(...), which returns the corresponding millisecond timestamp. Empty time components default to zero.
All conversions are performed in UTC to avoid time-zone and daylight-saving ambiguity, so the displayed clock values are wall-clock time at the prime meridian. Negative millisecond values represent dates before 1970. Invalid or non-numeric input, or a date string that is not in YYYY-MM-DD form, produces no result.
Frequently asked questions
Unix seconds count whole seconds since 1970-01-01 UTC, while milliseconds count thousandths of a second. To convert, multiply seconds by 1000 or divide milliseconds by 1000.
Unix time is defined relative to UTC, and using UTC avoids ambiguity from local time zones and daylight-saving changes, giving the same timestamp everywhere.
Yes. Dates before the Unix epoch produce negative millisecond values, which this converter handles correctly.
Also known as
TG we-Calculate Editorial Team. (2026). Unix Milliseconds Converter [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/unix-milliseconds-converter
TG we-Calculate Editorial Team. "Unix Milliseconds Converter." TG we-Calculate. 2026. https://we-calculate.com/calculator/unix-milliseconds-converter.
TG we-Calculate Editorial Team, "Unix Milliseconds Converter," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/unix-milliseconds-converter
@misc{wecalculate_unix_milliseconds_converter, title = {Unix Milliseconds Converter}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/unix-milliseconds-converter}}, year = {2026}, note = {TG we-Calculate} }
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