THE SHORT ANSWER
Divide the minutes by 60 before treating them as a decimal
1 hour 30 minutes is 1 + 30 ÷ 60 = 1.5 hours. Written as a decimal, 1.30 hours means 1 hour 18 minutes. Keep time notation separate from decimal hours, and convert to a common unit before adding.
Add 1 hour 30 minutes, 45 minutes, and 50 minutes
Suppose you studied for those three durations. Convert them to minutes: 90 + 45 + 50 = 185. Since 180 minutes is 3 hours, the total is 3 hours 5 minutes.
The same durations in hours:minutes
1:30 0:45 0:50
You can also add the minute parts: 30 + 45 + 50 = 125 minutes, or 2 hours 5 minutes. Add the original hour to get 3 hours 5 minutes. In decimal hours, 185 ÷ 60 is approximately 3.0833.
Choose hours:minutes and select “Try an example” in the Time Duration Sum Calculator to reproduce the total.
Why 1.30 hours is 12 minutes short of 1 hour 30 minutes
The decimal part is a fraction of an hour, not a number of minutes. Since 0.30 × 60 = 18, 1.30 hours is 1 hour 18 minutes. Replacing a colon with a decimal point does not convert the units.
Scroll sideways to see the full table.
| Duration | Hours:Minutes | Decimal hours |
|---|---|---|
| 15 minutes | 0:15 | 0.25 hours |
| 30 minutes | 0:30 | 0.5 hours |
| 45 minutes | 0:45 | 0.75 hours |
| 1 hour 30 minutes | 1:30 | 1.5 hours |
To go the other way, multiply decimal hours by 60. For example, 2.25 hours is 135 minutes, or 2 hours 15 minutes. Our duration-sum tool does not accept decimal inputs, so convert them to hours:minutes first.
A video’s 1:30 may mean minutes and seconds
In a work log, 1:30 might mean an hour and a half. For a short video, it might mean a minute and a half. The digits alone do not tell you which. Check the original units and use one format for every line you paste.
Video lengths in minutes:seconds
3:45 4:30 2:50
3 minutes 45 seconds, 4 minutes 30 seconds, and 2 minutes 50 seconds total 11 minutes 5 seconds. The seconds add up to 125, so you carry 2 minutes and keep 5 seconds. The calculator always displays its main result as hours:minutes:seconds: 0:11:05.
Add first, then round
Three 20-minute sessions total exactly 60 minutes, or 1 hour. If you first round each session to two decimal places, you get 0.33 hours. Multiplying that by three gives 0.99 hours—36 seconds short.
To avoid that difference, add the minutes or seconds first and convert the total afterward. Pattobako adds whole seconds, then displays converted minutes and decimal hours to four decimal places. Do not add rounded display values together when the original durations are available.
Three checks before you use the total
- Durations, not clock times. Adding a 9:00 start and a 10:30 finish will not give elapsed time. First work out the difference: 1 hour 30 minutes.
- Real repeats, not copied duplicates. Three lines of 0:20 count as three sessions. Remove accidental duplicate entries before adding.
- Overlapping periods. A 9–10 a.m. block and a 9:30–10:30 a.m. block add up to 2 hours of recorded durations, but span only 1 hour 30 minutes with the overlap counted once. The tool does not remove overlaps or subtract breaks.
If a line does not match your chosen format—for example, 1:60 or a decimal such as 1.5—the calculator identifies its line number and stops. It never silently drops an invalid duration to produce a partial total; only blank lines are skipped.