How to use the Time Unit Converter
- Enter the duration you want to convert.
- Select the unit it is currently in and the unit you want.
- Use days or smaller for anything precise — months and years are averages here.
- For calendar arithmetic between two real dates, use the date difference calculator instead.
- For payroll, convert minutes to decimal hours before entering them into a timesheet.
How the calculation works
Units up to the week are exact: 1,000 milliseconds to the second, 60 to the minute, 60 minutes to the hour, 24 hours to the day and seven days to the week. The second itself is the SI base unit, defined by 9,192,631,770 periods of a caesium-133 hyperfine transition, which makes every conversion in this range unambiguous.
Months and years are not exact and cannot be. A month is 28 to 31 days; this converter uses the Gregorian mean of 30.4375 days, derived from the 365.25-day Julian year divided by twelve. The year figure of 365.25 days matches the Julian convention still used for many interest and actuarial calculations. Choose day-based units whenever the answer will be used contractually.
Payroll deserves its own note because the conversion is where money quietly disappears. Timesheets want decimal hours, so 7 hours 45 minutes is 7.75 hours, not 7.45. Entering the latter loses 18 minutes per occurrence. Multiply minutes by 1/60 rather than shifting a decimal point, and the error class disappears entirely.
time_target = (t_source × s_per_source) ÷ s_per_target; min = 60 s; h = 3,600 s; d = 86,400 s; average month = 2,629,800 s; year = 31,557,600 sSource: BIPM SI Brochure 9th edition (definition of the second); ISO 80000-3; Gregorian calendar mean month.
Worked example
A service level agreement allows 43,200 seconds of downtime per year and you want that in familiar terms.
- Enter 43,200 and select seconds.
- Convert to hours: 43,200 ÷ 3,600 = 12 hours.
- Convert to days: 43,200 ÷ 86,400 = 0.5 days.
- As a fraction of a year: 43,200 ÷ 31,557,600 = 0.137%, so an availability target of 99.863%.
43,200 seconds is 12 hours a year — an availability of about 99.86%, which sits between the common three-nines and four-nines tiers.
Frequently asked questions
How many seconds in a day?+
86,400 in ordinary use. Very occasionally a leap second makes a real UTC day 86,401 seconds long, but leap seconds are being phased out by 2035.
How long is a month here?+
30.4375 days, the Gregorian average. Real months vary from 28 to 31 days, so use the date difference calculator for actual calendar spans.
Why 365.25 days in a year?+
It is the Julian convention, still standard in finance and actuarial work. The Gregorian mean is 365.2425 days, about 11 minutes shorter.
How do I convert minutes to decimal hours?+
Divide by 60. Forty-five minutes is 0.75 hours, not 0.45 — this is the most common payroll conversion error.
Last reviewed September 1, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.