Time Unit Converter (ms, s, min, h, days, weeks, months, years)
Type a duration and select its unit to see equivalents in every other supported unit. Useful for scheduling, billing, scientific calculations, and quick mental arithmetic.
How it works
Why months and years aren't exact
Seconds, minutes, hours, days, and weeks are exact: 1 minute is always 60 seconds, 1 day is always 86,400 seconds. Months and years are not — calendar months range from 28 to 31 days, and years can be 365 or 366 days. To convert at all, we have to pick a single average value.
This calculator uses the Julian year (365.25 days = 31,557,600 seconds), the standard in astronomy and the SI scientific community. The 'month' is one twelfth of a Julian year (30.4375 days = 2,629,800 seconds). These choices give consistent two-way conversions; they may differ from your calendar by a day or two.
What's exact and what isn't
Exact: ms ↔ s, s ↔ min, min ↔ h, h ↔ day, day ↔ week. These can be converted forward and back without losing any precision.
Approximate: any conversion involving 'month' or 'year', because the calendar values are not constant. If you need accurate calendar arithmetic ('how many days from March 1 to August 15'), use a date difference calculator instead — the time-unit converter is for averages.
Useful reference points
1 year ≈ 525,960 minutes ≈ 31.56 million seconds. 1 day = 1,440 minutes = 86,400 seconds. 1 week = 168 hours. 'A million seconds' ≈ 11.6 days; 'a billion seconds' ≈ 31.7 years. 1 hour of HD video ≈ 3.6 GB; 1 hour of audio ≈ 50 MB.
Frequently asked questions
›Why is the year 365.25 days?
We use the Julian year, the SI standard for astronomy. It's the average over the 4-year leap cycle. Calendar years vary by ±1 day; this is the long-run average.
›What's the month definition here?
1/12 of a Julian year, or 30.4375 days. It does not match any specific calendar month.
›Why did 1 minute → 60.0 s but 1 month → 30.4375 d?
Minutes are defined exactly. Months are calendar units that don't have a single fixed length, so we pick the long-run average for conversion.
›Is this accurate for billing or scheduling?
For exact calendar arithmetic, use a date difference calculator. For averages and rates ('hours per year'), this is the right tool.
›What about leap seconds?
Not modeled. Leap seconds happen rarely (~1 per 1.5 years on average) and are smaller than the rounding error from any month-or-year conversion.
›How precise are the smaller units?
ms ↔ s ↔ min ↔ h ↔ d are exact, displayed to up to 8 significant digits.
›Can I use this for video duration?
Yes. Film and video duration is just seconds-to-minutes-to-hours, which is exact.
›Can this replace a stopwatch?
It converts a known duration; it doesn't measure live time. For measuring elapsed time, use a stopwatch app or our countdown timer.
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