Duration Converter, Explained
After reading this you can turn any human-written duration like 1h 23m or 1:23:05 into an exact number of seconds, and turn a raw second count back into a readable duration, without guessing at the arithmetic.
What a duration converter does
A duration is a length of time with no fixed start or end. "90 minutes" is a duration. "3:00 PM" is not: that is a point in time. This tool works only with durations, and it works in both directions at once. Type 1h 23m and it reports 4980 seconds. Type 4980 seconds and it reports 1h 23m 0s, or 83 minutes, or 1.383 hours.
The single most useful thing it does is collapse every notation people actually write into one canonical number. Someone hands you a log that says 90 min, a spec that says 1.5h, and a stopwatch reading of 0:01:30:00. Those are the same length of time. Converted to seconds they are all 5400. Once everything is a second count you can add, compare and store durations without ambiguity.
When to use it, and when not
Use it whenever you need to compare or combine durations written in different formats, or when a system wants seconds and a human wrote something friendlier. Common cases: a video is 1:47:30 long and you need it in seconds for a subtitle offset, a workout plan lists 45 min blocks you want to total, or an API field expects an integer number of seconds.
Do not use it for anything that depends on the calendar. A duration converter treats one day as exactly 86400 seconds. Real calendar days are not always 86400 seconds long. The day a spring daylight saving change happens can be 82800 seconds (23 hours), and the autumn one 90000 seconds (25 hours). Leap seconds add one more second to a handful of days. If you need "the same wall-clock time tomorrow," that is a calendar operation, not a duration. For counting down to a fixed calendar moment, use the Countdown Generator instead.
Adding 24h to a timestamp is not the same as "tomorrow at the same time" across a daylight saving boundary. The duration is fixed at 86400 seconds; the wall clock is not. Keep duration math and calendar math separate.
The conversion, unit by unit
Every supported unit reduces to seconds through a fixed factor. There is nothing to estimate.
Here S is the total in seconds, d is days, h is hours, m is minutes and s is seconds. The factors come straight from the definitions: 60 seconds in a minute, 60 minutes (so 60 \times 60 = 3600 seconds) in an hour, and 24 hours (so 24 \times 3600 = 86400 seconds) in a day.
To go the other way, divide and take remainders. Start with a total S in seconds:
The floor brackets mean "round down to a whole number," and \bmod means "the remainder after dividing." So the days part is how many whole 86400-second blocks fit, and the hours part is how many whole 3600-second blocks fit in what is left over. Minutes and seconds follow the same pattern with 60 and 1. The full expansion is: m = \lfloor (S \bmod 3600) / 60 \rfloor and s = S \bmod 60.
| Unit | Seconds | In minutes | In hours |
|---|---|---|---|
| 1 second | 1 | 0.01667 | 0.0002778 |
| 1 minute | 60 | 1 | 0.01667 |
| 1 hour | 3600 | 60 | 1 |
| 1 day | 86400 | 1440 | 24 |
A worked example you can reproduce
Parsing 1h 23m
The demo loads 1h 23m. Here is the arithmetic the tool runs.
- Read the tokens:
1paired withh, and23paired withm. There are no day or second tokens, so d = 0 and s = 0. - Hours to seconds: 1 \times 3600 = 3600.
- Minutes to seconds: 23 \times 60 = 1380.
- Add them: 3600 + 1380 = 4980 seconds.
Now format 4980 back into every reading:
- Days: \lfloor 4980 / 86400 \rfloor = 0.
- Hours: \lfloor 4980 / 3600 \rfloor = 1, leaving 4980 - 3600 = 1380.
- Minutes: \lfloor 1380 / 60 \rfloor = 23, leaving 0.
- Seconds: 0. The canonical form is
1h 23m 0s.
As a single unit: 4980 / 60 = 83 minutes exactly, or 4980 / 3600 \approx 1.383 hours.
Reading the different output forms
One duration has several correct written forms, and they are not interchangeable in every context. Keep three ideas separate.
- Broken-down form
- The largest-unit-first breakdown, like
1h 23m 0s. Good for humans reading a single value. Never negative in any one field: the seconds field stays in the range 0 to 59. - Single-unit form
- The whole duration expressed in one unit, like
83 minor1.383 h. Good for spreadsheets and charts where every row must share a unit. May carry a fraction. - Clock form
- The colon notation
1:23:05, read right to left as seconds, minutes, hours. A leading1:23with two parts is minutes and seconds by that convention, so1:23is 83 seconds, not 83 minutes. Watch this closely; it is the most common misread.
When you share a duration with someone, prefer the broken-down form with explicit unit letters (1h 23m). It cannot be misread the way 1:23 can.
How the unit factors grow
The gap between units is not linear, and that trips up mental estimates. Each step up multiplies by 60, 60, then 24. The chart below shows how many seconds sit in one of each unit, on a scale where you can see the jumps.
Use the widget to feel the round trip. Move the total up and down and watch the broken-down form change one field at a time.
Common mistakes
Most errors come from unit confusion, not from the arithmetic itself.
- Reading clock form left to right.
1:30is 1 minute 30 seconds (90 seconds), not 1 hour 30 minutes. Add a field to force hours:1:30:00is one and a half hours (5400 seconds). - Treating "m" as months. In durations,
mis minutes. Months have no fixed second count (28 to 31 days), so this tool has no month unit at all. If a source means months, convert it to days first with a stated assumption. - Assuming a day is 24 hours in calendar math. It is here, by design, but real dates disagree twice a year in daylight saving zones. See the warning above.
- Losing precision with fractions.
1.383 hrounded to three decimals is 4978.8 seconds, not 4980. Keep the exact4980when you need to add many durations, and round only the final display.
Related tools
A duration is a length; a countdown is the shrinking gap to a fixed moment. To watch time run out toward a specific date, use the Countdown Generator. If you are laying out days, weeks or months on paper rather than measuring intervals, the Printable Calendar Generator produces clean monthly and yearly grids.
Frequently asked questions
How many seconds are in 90 minutes?
90 \times 60 = 5400 seconds. That is the same as 1h 30m and 1:30:00 in clock form.
Does the converter handle days and weeks?
It handles days, where one day is exactly 86400 seconds. It has no week or month unit because those either vary (months, 28 to 31 days) or are just seven days (a week is 7 \times 86400 = 604800 seconds, which you can enter as 7d).
Why does 1.5 hours not always come back as exactly 5400?
It does, because 1.5 is exact. The rounding problem appears with values like 1.383 h, which is a rounded display of 4980 seconds. If you re-enter the rounded number you get 4978.8 seconds. Store and add the second count, not the rounded hour figure.
Is 1:23 one hour or one minute?
By clock convention, two colon-separated parts are minutes and seconds, so 1:23 is 1 minute 23 seconds, which is 83 seconds. Three parts 1:23:05 are hours, minutes, seconds, which is 4985 seconds.
Does daylight saving affect the result?
No. This tool measures pure durations, so a day is always 86400 seconds and daylight saving is ignored. That matches how software timers and stopwatches behave. Calendar-aware math is a separate problem.
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