Time Converter
Convert between any two units of time — milliseconds to millennia, with documented conventions for "month" and "year" so the answer is unambiguous.
1 Hours (h) =
60
Converted via 3600 s per h and 60 s per min. Years use the Julian year of exactly 365.25 days (ISO 80000-3); a "common" year is 365 days and a Gregorian year is 365.2425 days. Months are the mean Julian month, 30.4375 days.
How to use this calculator
Enter a duration, choose its unit in the "From" dropdown, then pick the unit you want in the "To" dropdown. The result updates as you type.
How the calculation works
Every unit converts via a single intermediate value in seconds. We multiply the input by the seconds-per-unit factor for the source, then divide by the factor for the target. Sub-second SI prefixes follow ISO 80000-3. Day, week and fortnight are exact (1 day = 86,400 s). "Year" defaults to the Julian year of exactly 365.25 days = 31,557,600 s — the IUPAC / IUGS / ISO 80000-3 convention with symbol "a". The common year (365 d) and mean Gregorian year (365.2425 d) are exposed as separate units.
Worked example
2 hours → minutes: 2 × 3600 s/h = 7200 s, ÷ 60 s/min = 120 minutes. 1 Julian year → days: 31,557,600 s ÷ 86,400 s/day = 365.25 days exactly.
Frequently asked questions
How many seconds are in an hour?
An hour is exactly 3,600 seconds (60 minutes × 60 seconds). A day is exactly 86,400 seconds. These are SI definitions and not affected by leap seconds in the conversion — leap seconds adjust the relationship between UTC and astronomical time, not the unit "second".
Why is a year 365.25 days here?
We default to the Julian year of exactly 365.25 days = 31,557,600 seconds. This is the convention used by ISO 80000-3, IUPAC and the IAU — it averages out leap years over a four-year cycle. If you want a non-leap year, pick "Years (common, 365 d)". The mean Gregorian year (365.2425 d) accounts for the once-every-400-years rule and is also available.
How long is a "month"?
A calendar month varies from 28 to 31 days, so we use the mean Julian month: 365.25 / 12 = 30.4375 days = 2,629,800 seconds. This matches calculator.net and Wolfram Alpha. For exact calendar-month differences (e.g. "from 12 March to 12 May"), use a date-difference calculator instead — this converter assumes a uniform-length month.
What is a fortnight?
A fortnight is exactly 14 days = 1,209,600 seconds. The word survives in UK English (and in physics-classroom unit jokes like furlongs per fortnight), but is rare elsewhere. It is unambiguous: always 14 days.
Are leap seconds factored in?
No. Leap seconds are inserted irregularly to keep UTC aligned with the Earth's rotation, but they do not change the length of the unit "second" itself. Time conversions assume an idealised, leap-second-free timeline. The error from ignoring them is at most a few dozen seconds across all of recorded history.
How accurate are the results?
Conversions use full IEEE-754 double-precision arithmetic. All factors except "month", "year" and their multiples are exact. The Julian year is exact by definition (365.25 × 86,400 = 31,557,600 s). Only when comparing to an actual calendar (which has variable-length months and leap years) does the answer become an approximation.