Time Duration Converters

56 converters, all running in your browser.

Time conversions are exact up to the week and approximate beyond it, and the boundary matters.

A second, minute, hour, day and week are all fixed multiples of one another: 60, 60, 24 and 7. Above that the calendar intervenes. A month is 28, 29, 30 or 31 days, so "one month" has no fixed length — these converters use 30.44 days, the average across a year. A year is 365.25 days on average because of the leap-year cycle, and even that is an approximation: the Gregorian rule skips leap years in century years not divisible by 400, giving a mean of 365.2425 days.

For anything contractual — a notice period, an interest calculation, a subscription term — convert using real calendar arithmetic rather than an average. "Three months from 30 November" is a date, not a number of days, and the two answers differ.

All 56 converters

Conversion factors

From	To	Multiply by
Seconds	Milliseconds	1000
Seconds	Minutes	0.016666667
Seconds	Hours	2.7778e-4
Seconds	Days	1.1574e-5
Seconds	Weeks	1.6534e-6
Milliseconds	Seconds	0.001
Milliseconds	Minutes	1.6667e-5
Milliseconds	Hours	2.7778e-7
Milliseconds	Days	1.1574e-8
Milliseconds	Weeks	1.6534e-9
Minutes	Seconds	60
Minutes	Milliseconds	60000
Minutes	Hours	0.016666667
Minutes	Days	6.9444e-4
Minutes	Weeks	9.9206e-5
Hours	Seconds	3600
Hours	Milliseconds	3.6000e+6
Hours	Minutes	60
Hours	Days	0.041666667
Hours	Weeks	0.005952381

Where the Approximations Bite

Converting a duration is exact up to a week and approximate above it, and the approximation compounds in ways that matter for anything financial or contractual.

Interest is the clearest case. Lenders use several day-count conventions: 30/360 treats every month as 30 days and every year as 360, actual/365 uses real days against a fixed year, and actual/actual uses real days against a real year. The same loan produces different interest under each, and the difference over a long term is material.

Payroll is the other. A "monthly" salary paid twelve times a year and a "four-weekly" one paid thirteen times are different amounts for the same annual figure, and the thirteenth payment is where the confusion appears.

Useful Anchors

A year is about 8,766 hours, or 525,960 minutes.
A billion seconds is just under 32 years.
A million seconds is about 11.6 days.
10,000 hours — the figure attached to deliberate practice — is about 417 days of continuous

time, or roughly five years at four hours a day.

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