Quick answer: Time units scale by fixed factors: 1000 milliseconds per second, 60 seconds per minute, 60 minutes per hour, 24 hours per day, and 86,400 seconds per day. Weeks, months and years vary, so converters use averages of 30.44 days per month and 365.25 days per year to account for leap years.
Last reviewed: September 2026
Key facts
- 1 day = 86,400 seconds; 1 week = 604,800 seconds.
- 1 hour = 3,600 s; 1 minute = 60 s — the Babylonian base-60 system, still with us.
- A year averages 31,557,600 s (365.25 days, leap years included).
- 2.5 hours = 150 minutes = 9,000 seconds.
Seconds, minutes, hours, days, weeks — time units nest inside each other, and the maths is never as simple as it looks. This free time converter moves between milliseconds, seconds, minutes, hours, days, weeks, months and years instantly.
Enter a value and choose your units. Years and months use astronomical averages (365.25 days; 30.44 days) so long spans stay honest.
How to use
- Enter a value.
- Choose the from and to units.
- Read the answer and the full table of equivalents below.
How time conversion works
| Term | Meaning |
|---|---|
| from-unit in seconds | Each unit’s definition in seconds. |
| to-unit in seconds | The target unit’s definition in seconds. |
Months and years are averages (a month = 365.25 ÷ 12 ≈ 30.44 days) because real months vary in length.
Worked examples
Work and workouts
2.5 hours → minutes: 2.5 × 60 = 150 min.
2.5 hours → seconds: 2.5 × 3,600 = 9,000 s.
Big spans
1 week → seconds: 7 × 86,400 = 604,800 s.
90 minutes → hours: 90 ÷ 60 = 1.5 h — a football match plus half-time, roughly.
Time units in seconds
| Unit | Equals (s) | Notes |
|---|---|---|
| Millisecond (ms) | 0.001 | 1,000 per second |
| Second (s) | 1 | The SI base unit |
| Minute (min) | 60 | Base-60 heritage |
| Hour (h) | 3,600 | 60 minutes |
| Day | 86,400 | 24 hours |
| Week | 604,800 | 7 days |
| Month (average) | 2,629,746 | 365.25 ÷ 12 days |
| Year (average) | 31,557,600 | 365.25 days |
Frequently asked questions
How many seconds are in a day?
86,400 = 24 × 60 × 60. A useful number for programmers and puzzle fans.
How many seconds in a year?
31,536,000 in a common year; 31,622,400 in a leap year; 31,557,600 on the 365.25-day average.
Why 60 seconds in a minute?
The Babylonians used base 60 some 4,000 years ago, and the convention survived through Greek astronomy into modern timekeeping.
What is a millisecond?
One thousandth of a second. A camera flash lasts a few milliseconds; human reaction time is ~200 ms.
Why are months approximate?
Real months are 28–31 days. The converter uses the average (30.44 days) so month conversions are estimates — fine for planning, not for contracts.
Sources
Key takeaways
- 1 day = 86,400 s; 1 week = 604,800 s; 1 hour = 3,600 s.
- Years/months use averages (365.25 / 30.44 days) — exact for planning, approximate for contracts.
- The 60-based system is a 4,000-year-old Babylonian inheritance.
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