Time Unit Converter (ms, s, min, h, days, weeks, months, years)

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.