How time conversion works
To convert between any pair of time units, the simplest approach is to use seconds as an intermediate step. The input value is first turned into seconds, and that total is then converted into the desired target unit. That is exactly how this calculator works behind the scenes.
Conversion factors used
1 second = 1,000 milliseconds
1 minute = 60 seconds
1 hour = 60 minutes = 3,600 seconds
1 day = 24 hours = 86,400 seconds
1 week = 7 days = 604,800 seconds
1 month (average) = approximately 30.44 days = 2,629,746 seconds
1 year (average) = approximately 365.2425 days = 31,556,952 seconds
Worked example
A 90 minute meeting equals 5,400 seconds, since 90 multiplied by 60 seconds gives that value. In hours, the same 90 minutes correspond to 1.5 hours, because 90 divided by 60 equals 1.5.
Converting larger units (months and years)
Unlike seconds, minutes, hours, days and weeks, which have a fixed length, months and years vary in size on the common calendar. A month can have 28, 29, 30 or 31 days, and a leap year has one extra day compared to a common year. Because of this, for month and year conversions this calculator uses the Gregorian calendar average of 365.2425 days per year, which is the standard adopted by most time conversion tools.
Clock duration versus total time
When a stopwatch or a spreadsheet records a duration in hours:minutes:seconds format, it is often necessary to add everything into a single unit, usually seconds or decimal hours, to run calculations such as hourly pay or the sum of several activity durations. The duration calculator on this page does exactly that, combining hours, minutes and seconds into a single total.