Week Number Calculator
Time & Date · Free Online Tool
Calculate ISO 8601 week number for a date.
ISO 8601
Weeks start on Monday; week 1 contains the first Thursday.
Year-aware
Reports the ISO year, which can differ near January 1st.
Total Weeks
Shows how many ISO weeks the year contains (52 or 53).
How to Use Week Number Calculator
- 1Enter the time, date, or value you want to convert.
- 2Select the target format or timezone.
- 3The tool calculates the result instantly.
- 4Copy the converted value for your use.
Features
- ✓100% free — no signup, no subscription, no ads
- ✓Runs entirely in your browser — data never leaves your device
- ✓Fast and lightweight — instant results
- ✓Cross-platform — works on desktop, tablet, and mobile
Frequently Asked Questions
What timezone is used by default?
The Timestamp Converter uses UTC by default but can display results in your local timezone.
Can I convert timestamps from different programming languages?
Yes, the tool supports Unix timestamps (seconds and milliseconds), ISO 8601, and various date string formats.
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Learn the concept
Learn the concept
Understand the programming ideas behind this tool.