About the Week Number Calculator
Week Number Calculator helps you work with dates and timestamps. A Unix timestamp counts the seconds since 1 January 1970 (UTC) and is used throughout programming, databases and APIs. This tool converts Week Number accurately and shows both UTC and local results.
How Week Number works
The ISO 8601 week number identifies which week of the year a date falls in. Weeks start on Monday, and week 1 is the week containing the year’s first Thursday.
Worked example: 15 June 2025 falls in ISO Week 24 of 2025.
How to use
- Enter your value (a timestamp or a date).
- The converted result appears instantly, in UTC and local time.
- Click Copy to use it.
Common uses
- Debugging timestamps in logs and APIs.
- Converting between date and time formats.
- Calculating ages and date differences.
- Working with database date fields.
Frequently asked questions
Is the timestamp in seconds or milliseconds?
Unix timestamps are in seconds; this tool also shows milliseconds where relevant.
Which time zone is used?
Results are shown in both UTC and your browser's local time zone.