Three tools in one: convert between seconds, minutes, hours, days, weeks, months and years — add or subtract two durations — or find the exact duration between two times of day.
Convert mode converts any amount from one time unit to another — enter a number, choose the source unit and target unit, then click Calculate. Add / Subtract mode lets you add or subtract two durations expressed in hours, minutes and seconds. Difference mode finds the exact duration between two times of day, handling overnight spans automatically (e.g. 11 PM to 7 AM correctly returns 8 hours).