Time Duration Converter
Convert a length of time between ten units, from the millisecond up to the century. The small units are exact — sixty seconds to a minute, sixty minutes to an hour, twenty-four hours to a day. Months and years are trickier, because calendar months vary in length and years occasionally gain a leap day, so this converter uses Gregorian averages (a year of 365.2425 days, a month of one twelfth of that) for consistent results.
How to use this tool
- Type the duration you want to convert into the Value field.
- Pick the unit your number is currently in from the From menu.
- Pick the unit you want the answer in from the To menu.
- Read the result as you type — there is no button to press.
- Switch on “Show every equivalent unit” to see the same duration across all ten units.
The formula
Time uses the second as its base unit. Units up to a week are exact. Months and years are not, because the calendar does not divide evenly, so this converter uses defined averages.
seconds = value × seconds_per_unit
result = seconds ÷ seconds_per_target- seconds_per_unit
- Seconds in one unit of the input
- year
- 365.2425 days — the Gregorian mean, including leap rules
- month
- One twelfth of a Gregorian year, about 30.44 days
The Gregorian calendar adds a leap day every four years, except century years not divisible by 400. That averages to 365.2425 days per year. For counting real days between two dates, use a date calculator instead — averages do not answer that question.
Worked examples
Hours to minutes
- Given
- 2 hours
- Result
- 120 minutes
2 h × 60 minutes per hour = 120 minutes. Hours, minutes and seconds are all exact.
Days in a year
- Given
- 1 year
- Result
- 365.242500 days
This converter uses the Gregorian mean year of 365.2425 days, which averages in the leap-year rule, rather than a flat 365.
Seconds in a week
- Given
- 1 week
- Result
- 604800 seconds
7 days × 24 hours × 60 minutes × 60 seconds = 604,800 seconds, exactly.
Frequently asked questions
One twelfth of a Gregorian average year — about 30.44 days. Real calendar months range from 28 to 31 days, so if you need an exact number of days between two dates, use a date-difference calculator instead. The average is used here to give a consistent figure for converting durations.
Because of leap years. The Gregorian calendar adds a leap day most years divisible by four, with century exceptions, averaging out to 365.2425 days per year. Using this average means converting, say, seconds to years stays consistent rather than drifting.
Yes. There are exactly 60 seconds in a minute, 60 minutes in an hour and 24 hours in a day, so conversions among these units and down to milliseconds carry no approximation.
Yes — enter 90, set From to minutes and To to hours, and you get 1.5 hours. The converter handles any decimal result, and the “show every equivalent” option lays the same duration out across all units at once.
The century, equal to 100 average Gregorian years. Along with the decade, it is useful for expressing very long spans compactly. For scientific timescales beyond that you would typically switch to years in scientific notation.
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