Time unit conversion table
Each unit in seconds and in days, with the exact units separated from the two conventional ones.
| Unit | Seconds | In days | Exact? |
|---|---|---|---|
| 1 second | 1 | 0.000011574074 | Exact |
| 1 minute | 60 | 0.00069444444 | Exact |
| 1 hour | 3,600 | 0.041666667 | Exact |
| 1 day | 86,400 | 1 | Exact |
| 1 week | 604,800 | 7 | Exact |
| 1 month | 2,629,800 | 30.4375 | Convention |
| 1 year | 31,557,600 | 365.25 | Julian year |
- The month here is an average, not a calendar month. No actual month is 30.4375 days long — the value is one twelfth of a Julian year, which is what makes twelve of them reconstruct a year exactly.
- The Julian year of 365.25 days is the IAU-defined unit of time and the basis of the light-year. The Gregorian mean calendar year is 365.2425 days; the difference is about eleven minutes a year.
- The day is fixed at exactly 86,400 seconds. The Earth's actual rotation drifts against that, which is why leap seconds were inserted into UTC 27 times between 1972 and 2016; the International Bureau of Weights and Measures has resolved to stop using them by 2035.
What is a time unit conversion?
A duration conversion rescales an amount of elapsed time. The second is the SI base unit, defined since 1967 by the caesium-133 hyperfine transition frequency of 9,192,631,770 Hz. Every unit up to the week is an exact multiple of it: 60 seconds to the minute, 60 minutes to the hour, 24 hours to the day and 7 days to the week.
Beyond the week the exactness stops. Calendar months run from 28 to 31 days and calendar years from 365 to 366, so converting a duration into months or years requires choosing an average. This converter uses the Julian year of exactly 365.25 days — the unit of time defined by the International Astronomical Union and the one behind the light-year — and takes the month as one twelfth of it, 30.4375 days.
The alternative convention is the Gregorian mean calendar year of 365.2425 days, which accounts for the century leap-year rule. The two differ by about 0.002%, roughly eleven minutes per year: immaterial for a duration of weeks, worth knowing for one spanning centuries. This converter is for durations, not for dates — to count the days between two calendar dates, including real leap years, use the date calculators on this site.
How to use this time unit converter
- Enter the duration you want to convert.
- Select its unit, from milliseconds up to years.
- Read the equivalent in every other unit at once.
- For anything anchored to real calendar dates — an age, a deadline, a project schedule — use a date calculator instead, so real month lengths and leap years apply.
The conversion factors behind the time converter
The duration is converted to seconds, then divided by each target unit's length in seconds. The first five factors are exact; the month and year are the stated conventions.
Worked example: 90 minutes = 90 × 60 = 5,400 seconds. In hours: 5,400 ÷ 3,600 = 1.5 h. In days: 5,400 ÷ 86,400 = 0.0625 day. In weeks: 5,400 ÷ 604,800 = 0.0089285714 week.
Common mistakes
- Using this converter for calendar arithmetic. Three months from 31 January is not 91.3 days in any useful sense — a date calculator handles real month lengths.
- Assuming a month is 30 days. That convention exists in finance, but it makes twelve months 360 days, five and a quarter days short of a year.
- Reading decimal hours as hours and minutes. 1.5 hours is one hour thirty minutes; 1.5 is not 1 h 5 min.
- Mixing the Julian and Gregorian year definitions inside one calculation over long spans, where the eleven-minute annual difference accumulates.
Часто задаваемые вопросы
How many seconds are in a day?
Exactly 86,400 — 24 hours of 60 minutes of 60 seconds. This is the definition of the day as a unit of time. The Earth's actual rotation period drifts slightly against it, which is what leap seconds in UTC corrected for until their planned retirement by 2035.
How many days are in a month?
Calendar months run from 28 to 31 days, so a converter has to choose an average. This one uses 30.4375 days, one twelfth of a Julian year, so that twelve months reconstruct a year exactly. For anything tied to real dates, use a date calculator rather than an average.
Why is a year 365.25 days here?
That is the Julian year, the unit of time defined by the International Astronomical Union and the basis of the light-year. The Gregorian mean calendar year, which includes the century leap-year rule, is 365.2425 days. The two differ by about eleven minutes a year — negligible for short durations, and stated here so you know which you have.
How many hours is 90 minutes?
1.5 hours. Divide minutes by 60: 90 ÷ 60 = 1.5. Note that 1.5 hours means one hour and thirty minutes, not one hour and five minutes — decimal hours and hours-and-minutes are different notations, and confusing them is the most common error in timesheets.
What is the difference between this and a date calculator?
This converts a duration — an amount of elapsed time — using fixed unit lengths. A date calculator works between two calendar dates and applies real month lengths and leap years. Use this to turn 5,400 seconds into hours; use a date calculator to find how many days until a specific date.
Источники
- Bureau International des Poids et Mesures (BIPM). The International System of Units (SI Brochure), 9th edition, 2019 — definition of the second, and the minute, hour and day as non-SI units accepted for use with the SI.
- International Astronomical Union. IAU (1976) System of Astronomical Constants — the Julian year of exactly 365.25 days, the basis of the light-year.