Time Calculator

How to use?

Time units and conversions

The SI base unit of time is the second (s), defined since 1967 as the duration of 9,192,631,770 periods of the radiation emitted by the caesium-133 atom in a specific hyperfine transition. From the second, the usual conversions follow: 1 min = 60 s, 1 h = 3,600 s, 1 day = 86,400 s, 1 Julian year = 365.25 days = 31,557,600 s. The Gregorian calendar (1582) uses 365-day common years and 366-day leap years (years divisible by 4, except centuries not divisible by 400). Time conventions in computing rely on UTC (Coordinated Universal Time), local time zones (UTC offsets) and, in some countries, daylight saving time. To sum durations in HH:MM:SS, add seconds, carry every 60 seconds into the minutes column and every 60 minutes into the hours column — the same sexagesimal logic used since the Babylonians.

Applications

Project scheduling (PERT/CPM, Gantt charts), CLT timesheets and the 8-hour Brazilian working day, sports timing and pace, physics problems, audio/video editing (frame and clip durations), and computing systems based on Unix epoch time (seconds since 1970-01-01 UTC).

FAQ

How many seconds are there in a day? 86,400 (= 24 × 3,600). Note that on days with leap seconds the official day can have 86,401 s.

What is a Julian year? Exactly 365.25 days (31,557,600 s), the average length used in astronomy. The mean Gregorian year is 365.2425 days.

How do I add HH:MM:SS values? Sum seconds, then minutes, then hours; whenever seconds or minutes reach 60, carry 1 to the next column.

Why is time sexagesimal? The 60-base system for minutes and seconds comes from Babylonian astronomy and was preserved through Hellenistic, Islamic and European traditions.