Units of time
Time units follow an old mix of bases. Sixty seconds make a minute and sixty minutes an hour, a base-60 system inherited from ancient astronomy. Twenty-four hours make a day and seven days a week. Months and years are tied to the Moon and the Sun, so their lengths vary, while milliseconds bring the decimal system to very short durations.
How to use this converter
Type a duration in any field and every other unit updates instantly. You can enter decimals, such as 1.5 hours or 0.75 days. Each common pair below the converter has its own page with the formula, a worked example and a chart.
Fixed and average units
- 1 minute = 60 seconds, 1 hour = 3,600 seconds
- 1 day = 24 hours = 1,440 minutes = 86,400 seconds
- 1 week = 7 days = 168 hours
- 1 average month = 30.436875 days
- 1 average year = 365.2425 days ≈ 52.18 weeks
The second through the week are exact. Months and years are averages over the Gregorian calendar, so converting 1 year gives 365.24 days rather than 365. That is the right answer over long periods, such as converting an age or a loan term, but for a specific date range you should count the actual days.
Decimal time versus clock time
A decimal result such as 2.5 hours means two and a half hours, that is 2 hours 30 minutes, not 2 hours 50 minutes. To go from decimal to clock time, multiply the decimal part by 60. Timesheets and payroll software often store hours as decimals: 15 minutes is 0.25 h, 20 minutes 0.333 h and 45 minutes 0.75 h.
Tips
For durations shorter than a second, milliseconds are easier to read than long decimals of a second. For very long periods, prefer years: a billion seconds is about 31.7 years.
Time units compared
| Unit | Symbol | In seconds |
|---|---|---|
| Millisecond | ms | 0.001 |
| Second | s | 1 |
| Minute | min | 60 |
| Hour | h | 3,600 |
| Day | d | 86,400 |
| Week | wk | 604,800 |
| Month | mo | 2,629,746 |
| Year | yr | 31,556,952 |
The units in detail
What is a millisecond?
The millisecond is one thousandth of a second. It measures reaction times (about 200 to 300 ms for a person), network latency, camera shutter speeds and the timing of computer programs.
What is a second?
The second is the SI base unit of time, defined from the vibration frequency of the cesium-133 atom. A minute has 60 seconds, an hour 3,600 and a day 86,400.
What is a minute?
The minute equals 60 seconds. It is the everyday unit for cooking times, commutes, meetings and phone plans. The base-60 split of the hour goes back to Babylonian astronomy.
What is an hour?
The hour equals 60 minutes or 3,600 seconds. Work time, pay rates, parking and travel durations are counted in hours; a full-time US work week is usually 40 hours.
What is a day?
The day equals 24 hours or 86,400 seconds. It is the natural unit for deadlines, rentals, notice periods and medication courses. The occasional leap seconds added to official clocks are ignored here.
What is a week?
The week is 7 days or 168 hours. Pregnancies, payroll periods, training plans and project schedules are often counted in weeks. A year has a little over 52 weeks.
What is a month?
Calendar months last 28 to 31 days, so this converter uses the average Gregorian month of 30.436875 days, one twelfth of an average year. For an exact count between two dates, count the actual days instead.
What is a year?
A calendar year has 365 days, or 366 in a leap year. This converter uses the average Gregorian year of 365.2425 days, which accounts for leap years over a 400-year cycle. Astronomers use slightly different year lengths.