Unix Timestamp Converter

Tool guide

What is Unix Timestamp Converter?

Unix Timestamp Converter moves between seconds, milliseconds, and timezone-qualified ISO dates without guessing the unit from digit length. Results can be shown in UTC or the browser's local zone. Date-to-timestamp input must include Z or an offset to avoid ambiguity around daylight-saving transitions and local clock times. Common workflows include the following. Turn Unix seconds from a log into readable time. Generate millisecond timestamps for an API request. Compare the same instant in UTC and local time. The page also documents input boundaries, output behavior, and practical cautions so you can review the result before putting it into an application, configuration, test, or production workflow.

When to use it

Turn Unix seconds from a log into readable time.
Generate millisecond timestamps for an API request.
Compare the same instant in UTC and local time.

How to use it

Select seconds or milliseconds and the display timezone.
Enter an integer timestamp, or an ISO date-time with Z or an offset.
Run the required conversion and copy the result.
Load one of the realistic examples first to verify the selected options and processing direction before replacing it with your own data.
Review the output, status message, and documented limits; copy, download, or continue only after the result matches your expectation.

Runnable examples

The “Example 1” and “Example 2” buttons load the matching inputs. They cover different structures, directions, or boundaries and can be run directly in the workspace.

Example 1

1735689600

Example 2

2026-08-09T03:15:00+08:00

Input rules

A timestamp must be an integer with seconds or milliseconds selected explicitly.
Date input must be parseable ISO text ending in Z or a timezone offset.
Values outside the JavaScript Date range are rejected.
Text input is counted before processing and is limited to 100 characters on this page; file modes apply the separate file limit shown in the workspace.
Date-to-timestamp input must end in Z or an explicit offset such as +08:00.

Output rules

Timestamp-to-date provides standard ISO and selected-zone displays.
Date-to-timestamp returns explicit seconds and milliseconds.
Changing the display zone does not change the represented instant.
Output reflects only the current input, direction, and options; rerun after changing a mode or value instead of treating an earlier result as current.
Leap seconds are not represented by JavaScript Date.

Limitations and cautions

Date-to-timestamp input must end in Z or an explicit offset such as +08:00.
Leap seconds are not represented by JavaScript Date.
Supported dates are limited to the JavaScript Date range.

How your data is handled

Parsing and conversion use local browser date functions and do not send time data to a server.

FAQ

Why must I choose seconds or milliseconds?

Digit-count guessing becomes unreliable for historical and far-future dates, so the tool requires an explicit unit.

Why is a timezone required for date input?

A local clock value can be ambiguous or nonexistent around daylight-saving changes.

Does local display change the timestamp?

No. It changes only how the same instant is displayed.

What happens if I choose the wrong unit?

The same integer becomes a completely different instant, so the page requires seconds or milliseconds explicitly.

Why do UTC and local time look different?

They display the same instant in different time zones; changing the display zone does not change the timestamp.

Why must date input include Z or an offset?

A local wall-clock time can be repeated or missing around daylight-saving changes, so an explicit offset prevents guessing.