Convert 1000 seconds to UTC ISO format
Input and settings
Direction: Unix→date / Unit: seconds / Value: 1000
Expected result
1970-01-01T00:16:40.000Z
Unix Timestamp Converter
Convert between Unix timestamps and ISO date-time values in seconds or milliseconds.
How to use
- Choose timestamp-to-date or date-to-timestamp.
- Enter the value and select seconds or milliseconds.
- Check the resulting date/time and unit before copying.
Enter values
Conversion result
About this tool
Convert Unix time measured from 1970-01-01 00:00:00 UTC into an unambiguous ISO 8601 value, with explicit seconds or milliseconds.
A date string without a timezone is interpreted in the device's local zone. Add Z to specify UTC explicitly.
Seconds and milliseconds use different digit lengths for the same UTC time
2026-01-01T00:00:00.000Z is 1767225600 in Unix seconds and 1767225600000 in Unix milliseconds. Selecting the wrong unit creates a factor-of-1000 error.
- The trailing Z identifies UTC. For date-time input without an explicit zone, verify how the browser interprets the value.
- Very large values and distant dates are limited by the range and precision of JavaScript Date.
Try a use case and check the result
Use fixed values to check seconds versus milliseconds and rounding before the Unix epoch.
Example buttons replace the inputs and settings above and calculate. Restore previous input steps back one example at a time. After trying multiple examples, repeat restore to return to your original input. This history is lost when the page closes.
Convert half a second before the epoch to whole seconds
Input and settings
Direction: date→Unix / Unit: seconds 1969-12-31T23:59:59.500Z
Expected result
-1 second / In milliseconds: -500
How to read the result
Z means UTC. Interpreting 1000 as milliseconds instead gives 00:00:01.000Z, a factor of 1000 difference. Date-to-seconds uses floor rounding, so −0.5 becomes −1, not zero. Milliseconds preserve the value −500.
Scope and limits
Supply Z or an explicit offset. Date-time strings without an offset depend on the device zone and are interpreted differently from date-only strings. The existing Date.parse parser is not strict ISO validation and may normalize some invalid dates. UTC output does not include a regional zone name. Leap seconds are unsupported.
Verification: calculation checks compare unit scaling, floor rounding before the epoch and equal instants with explicit offsets. Browsers in three zones distinguish explicit-offset and offsetless inputs and check restoration after mode changes.
Continue with the next task
Before changing conversion direction
To convert to a date, choose Unix time → date and enter the number with its seconds or milliseconds unit. For the reverse direction, enter a date-time string. Changing direction resets the input to a default value, so keep any value you need before switching.
Handling input values
Numbers and date-time strings are not autosaved. Conversion uses the browser’s Date implementation; the tool does not send input values to a date-conversion service.
Frequently asked questions
What is the difference between 10 and 13 digits?
Ten digits usually represent seconds and 13 usually represent milliseconds; select the matching unit.
Is the output in UTC?
Timestamp-to-date output uses UTC ISO format.
Are leap seconds represented?
No. It follows standard JavaScript date behavior.
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