Time Unit Converter

How the converter works

Each unit is stored as a number of seconds: a minute is 60, an hour 3,600, a day 86,400 and a week 604,800. These are exact. Months and years are not fixed lengths — a month runs 28 to 31 days and a year 365 or 366 — so the converter uses the long-run Gregorian averages: a year of 365.2425 days (31,556,952 seconds) and a month of one twelfth of that, 30.436875 days (2,629,746 seconds).

result = value × (seconds per source unit) ÷ (seconds per target unit)
average year = 365.2425 d · average month = 30.436875 d

The 365.2425 figure comes from the Gregorian leap-year rule: 97 leap days every 400 years, so (400 × 365 + 97) ÷ 400 = 365.2425.

Worked examples

Example 1: 10,000 minutes in hours

10,000 × 60 ÷ 3,600 = 166.666667 hours, which is 6 days 22 h 40 min.

Example 2: one billion seconds in years

1,000,000,000 ÷ 31,556,952 = 31.688739 years, a milestone people reach at about age 31 years and 8 months.

Example 3: 90 days in weeks

90 × 86,400 ÷ 604,800 = 12.857143 weeks, i.e. 12 weeks and 6 days.

Example 4: 250 milliseconds

250 ms is 0.25 seconds, about the duration of a typical human reaction to a visual signal.

How to read the result

The headline shows the time in your chosen unit and the formula line the multiplier. The table converts the same span into every unit, with average months and years labelled as averages. Below the table, spans of a minute or more are also written as days, hours, minutes and seconds, which is often the most natural way to read them.

When averages are not enough

For anything tied to real calendar dates — rent periods, contract terms, ages, deadlines — months and years should be counted on the calendar, not with averages. "Six months from 31 August" is a specific date, not 182.62 days. For those jobs use the add or subtract days calculator or the days between dates calculator. Astronomers use a Julian year of exactly 365.25 days, and a tropical year (equinox to equinox) is about 365.2422 days; these differ slightly from the Gregorian average used here.

Common uses

Time conversions are handy for turning a number of minutes from a fitness app into hours, expressing a project estimate in working weeks, converting video or audio lengths, reading computer timeouts and latencies in milliseconds, comparing subscription terms, and turning seconds-based timestamps or durations into something human-readable. For clock-time intervals between two times, the time duration calculator is the better tool.

Limits

Days are treated as exactly 86,400 seconds. Real calendar days can be 23 or 25 hours long at daylight-saving changes, and leap seconds have occasionally been added to UTC, though ordinary device clocks smooth them out. Working days, school terms and business hours are not modelled — a "working week" is usually 5 days or about 40 hours, so divide by those figures instead if that is what you mean.

Large numbers of seconds and milliseconds

Computers often record time as a count of seconds or milliseconds since a reference moment. Unix time, for example, counts seconds since 00:00 UTC on 1 January 1970, and JavaScript uses milliseconds from the same moment. A duration from such systems — a cache lifetime of 86,400 seconds, a timeout of 30,000 milliseconds — is much easier to understand once converted: those are one day and 30 seconds respectively. The converter handles values up to around a trillion seconds, more than 31,000 years, while still breaking smaller spans into days, hours, minutes and seconds.

Time arithmetic tips

Time units are not decimal above the second, so always convert before adding or subtracting. Adding 1 h 50 min and 2 h 25 min gives 4 h 15 min, not 3.75 or 4.75. The safest method is to convert everything to the smallest unit involved, do the arithmetic, then convert back. When averaging lap or task times, convert each to seconds first, take the mean with the average calculator, and convert the result back here.

Weeks, fortnights and working time

Some units in common use are not in the list but are easy to derive. A fortnight is 14 days, or 336 hours. A quarter is a quarter of a year: about 91.31 days on the Gregorian average, though calendar quarters run 90 to 92 days. A standard full-time working year is often approximated as 52 weeks of 40 hours, 2,080 hours, before holidays and leave; dividing an annual salary by 2,080 is a common way to estimate an hourly equivalent.