Days and 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.
A week is exactly 7 days. Pregnancy, project plans, payroll cycles and training programs are counted in weeks.
Worked example
Convert 100 d: 100 × 0.1428571429 = 14.28571429, so 100 days is 14.28571429 weeks. Likewise 200 d = 28.57142857 wk.
Estimating in your head
Divide by 7 for a quick figure; it is off by about 0%. For 100 d that gives 14.3 wk, against 14.2857 exactly.
Going the other way
To convert weeks to days, divide by 0.1428571429 (or multiply by 7). The swap button between the boxes opens that page.
How this works
wk = d × 0.1428571429
1 d = 86,400 s and 1 wk = 604,800 s, both by definition, so the factor is their ratio: 0.1428571429 (rounded here; the page uses the full value). 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 weeks are in a day?
1 day = 0.1428571429 weeks. The factor is exact by definition but has endless decimals, so it is shown rounded; the page uses the full value.
How do I convert days to weeks?
Multiply by 0.1428571429. For example, 200 d × 0.1428571429 = 28.57142857 wk.
What is 1,000 d in weeks?
1,000 d = 142.8571429 wk. 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/days-to-weeks/