Weeks and days
A week is exactly 7 days. Pregnancy, project plans, payroll cycles and training programs are counted in weeks.
A day here is 24 hours, or 86,400 seconds; it ignores the rare leap second. Deadlines, rental periods, shipping times and interest calculations are counted in days.
Worked example
Convert 40 wk: 40 × 7 = 280, so 40 weeks is 280 days. Likewise 20 wk = 140 d.
Estimating in your head
The factor is a short exact number, so mental math needs no rounding: multiply by 7.
Going the other way
To convert days to weeks, divide by 7 (or multiply by 0.142857142857). The swap button between the boxes opens that page.
How this works
d = wk × 7
1 wk = 604,800 s and 1 d = 86,400 s, both by definition, so the factor is their ratio: 7 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many days are in a week?
1 week = 7 days, exactly. The value follows from the unit definitions, so it never changes.
How do I convert weeks to days?
Multiply by 7. For example, 20 wk × 7 = 140 d.
What is 100 wk in days?
100 wk = 700 d. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- BIPM — The International System of Units (SI Brochure), 9th edition
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- Wikipedia — Gregorian calendar
Reviewed Oct 17, 2026 · test vectors fixtures/units/time/weeks-to-days/