Time Converter: Seconds, Hours, Days, Months, Years and Decimal Hours

Seconds are the base. A minute is 60 seconds, an hour is 3,600 seconds and a day is 86,400 seconds; NIST lists the minute, hour and day among the units accepted for use with the SI. A week is seven days, which is 604,800 seconds. Leap seconds are ignored, so a day here is always exactly 86,400 seconds. The tool converts lengths of time, not clock times, so daylight saving does not come into it.

Months and years are not fixed, so the tool lists the choices. The average Gregorian year is 365.2425 days: a 400-year cycle holds 97 leap years, so it has 303 x 365 + 97 x 366 = 146,097 days, and 146,097 divided by 400 is 365.2425. The average Gregorian month is 365.2425 divided by 12 = 30.436875 days, which is 2,629,746 seconds. Many payrolls and contracts use a 30-day month or a 365-day year instead (NIST lists a 365-day year as 3.1536 x 10^7 seconds, which is 365 x 86,400 = 31,536,000), so both are in the list too. A real calendar month is 28 to 31 days; for the exact gap between two dates use the date difference calculator.

Timesheets often need decimal hours: 7.75 instead of 7:45. Divide the minutes by 60. 45 minutes is 0.75 hours, so 7:45 is 7.75 hours. 20 minutes is 0.3333 hours, so 8:20 is 8.3333 hours. When you enter several times the tool adds them in whole seconds and rounds once at the end, so three shifts of 8:20 add up to exactly 25:00, which is 25 hours, where three rounded lines of 8.33 would give 24.99. Rounding rules such as the nearest quarter hour are an employer or payroll decision, so check yours.

The reverse helpers work the same way. Multiply the decimal part of an hour by 60 to get minutes: 0.6 hours is 36 minutes, so 2.6 hours is 2:36:00. A value that is not a whole number of seconds is rounded to the nearest second, and the page tells you when that happens. Minutes to hours and minutes divides by 60 and keeps the remainder: 135 minutes is 2 h 15 min, and 135.5 minutes is 2 h 15 min 30 s.