Fixed and average units
Seconds, minutes, hours, days and weeks have fixed lengths here: 60 seconds, 60 minutes, 24 hours, 7 days. Months and years do not, so the converter uses the average of the Gregorian calendar: a year of 365.2425 days, which counts the leap years over a 400-year cycle, and a month of a twelfth of that, 30.436875 days.
When to use a calendar instead
Averages suit rates and long spans, like the number of seconds in a year (31,556,952). For a particular stretch of dates, the Date Calculator counts the real days between them, and for hours on a clock the Hours Calculator works out the time between a start and an end.
Questions
How many hours are in a week?
168: 7 days of 24 hours. A 40-hour working week is 23.8% of it.
Why is a year 365.2425 days, not 365?
Three years in four have 365 days and the fourth has 366, except century years not divisible by 400. Averaged over 400 years that is 365.2425 days. A plain 365-day year is 31,536,000 seconds.