How to convert time units
Choose the unit you have in From and the unit you want in To, enter a number and press Convert. The value must be a single decimal number, so a duration like 1:30 has to be entered as 1.5 hours or 90 minutes. Negative durations are rejected.
How the conversion works
Every unit is stored as a number of seconds. The SI second is defined by the frequency of a transition in the caesium-133 atom, 9,192,631,770 hertz. From there the everyday units are fixed multiples: a minute is 60 s, an hour 3,600 s, a day 86,400 s and a week 604,800 s. A fortnight is two weeks.
Months and years are different, because calendar months run from 28 to 31 days and years have 365 or 366 days. The converter therefore offers year units with stated lengths and uses averages for the month, decade, century and millennium:
| Unit | Days | Hours | Seconds | Meaning |
|---|---|---|---|---|
| Common year | 365 | 8760 | 31536000 | Calendar year without a leap day |
| Julian year | 365.25 | 8766 | 31557600 | Julian calendar average; used in astronomy |
| Average Gregorian year | 365.2425 | 8765.82 | 31556952 | Average of the calendar in use today |
| Average Gregorian month | 30.436875 | 730.485 | 2629746 | One twelfth of the Gregorian year |
The Gregorian calendar adds a leap day in years divisible by 4, except century years not divisible by 400: 1900 was not a leap year, but 2000 was. That gives 97 leap years in every 400, or 146,097 days, and 146,097 ÷ 400 = 365.2425 days per year. The older Julian calendar added a leap day every four years, for an average of 365.25 days, which means 3 more leap days than the Gregorian calendar every 400 years.
Worked examples
- 90 minutes to hours: 90 ÷ 60 = 1.5 h.
- 2.75 hours to hours and minutes: keep the 2 hours and convert the rest, 0.75 × 60 = 45, so 2 h 45 min.
- 1,000,000 seconds to days: 1,000,000 ÷ 86,400 ≈ 11.574 days. Splitting the remainder gives 11 days 13 h 46 min 40 s.
- 1 billion seconds to years: 1,000,000,000 ÷ 31,556,952 ≈ 31.69 average Gregorian years.
Minutes to decimal hours
| min | h |
|---|---|
| 6 | 0.1 |
| 10 | 0.167 |
| 15 | 0.25 |
| 20 | 0.333 |
| 30 | 0.5 |
| 40 | 0.667 |
| 45 | 0.75 |
| 50 | 0.833 |
Hours to minutes and seconds
| h | min | s |
|---|---|---|
| 0.25 | 15 | 900 |
| 0.5 | 30 | 1800 |
| 1 | 60 | 3600 |
| 1.5 | 90 | 5400 |
| 2 | 120 | 7200 |
| 8 | 480 | 28800 |
| 24 | 1440 | 86400 |
Units that are easy to confuse
- Calendar months and the average month. The month here is 30.436875 days. A real month is 28, 29, 30 or 31 days, so three average months (about 91.31 days) do not match January to March, which has 90 or 91.
- Which year? A 365-day year is 31,536,000 s, the Julian year 31,557,600 s and the average Gregorian year 31,556,952 s. A leap year of 366 days is 31,622,400 s. Pick the definition your source uses.
- Decades and centuries. These are multiples of the average Gregorian year, so a decade is 3,652.425 days. An actual ten-year span usually contains 3,652 or 3,653 days, depending on how many leap days it includes.
- Clock days. The converter treats every day as exactly 24 hours. On days when clocks change for daylight saving time, the local day has 23 or 25 hours, and a UTC day with a leap second has 86,401 s.
Common mistakes
- Reading decimal hours as minutes. On a timesheet, 7 h 45 min is 7.75 h, while 7.45 h is only 7 h 27 min. The minutes table above helps with this.
- Using averages for dates. Average months do not follow the calendar: one average month after midnight on 1 February ends on 3 March in a common year. For calendar dates, count actual days; for Unix time, use the timestamp converter.
- Mixing prefixes. A millisecond (ms) is a thousandth of a second, a microsecond (µs) a millionth and a nanosecond (ns) a billionth. A frame at 60 frames per second lasts about 16.67 ms.
Frequently asked questions
How many weeks are in a year?
A 365-day year is 52 weeks and 1 day, about 52.143 weeks; a leap year is 52 weeks and 2 days. The average Gregorian year is 52.1775 weeks.
How many hours are in a year?
8,760 in a 365-day year and 8,784 in a leap year. The average Gregorian year has 8,765.82 hours.
How many days are in a month on average?
30.436875 days, or 730.485 hours, which is 365.2425 ÷ 12.
Why does the converter not accept 1:30?
It converts one number between two units. Convert the hours and minutes into one unit first: 1:30 is 1 + 30 ÷ 60 = 1.5 hours.
Supported units
- Nanosecond (ns)
- Microsecond (µs)
- Millisecond (ms)
- Second (s)
- Minute (min)
- Hour (h)
- Day (d)
- Week (wk)
- Fortnight (fortnight)
- Month (average Gregorian) (mo)
- Year (average Gregorian, 365.2425 days) (yr)
- Year (common, 365 days) (yr (365 d))
- Year (Julian, 365.25 days) (yr (Julian))
- Decade (average Gregorian) (decade)
- Century (average Gregorian) (century)
- Millennium (average Gregorian) (millennium)