Quick answer
Add minutes divided by 60 and seconds divided by 3,600 to the whole hours. To reverse it, multiply the fractional hour by 60 for minutes, or by 3,600 for seconds.
Step by step
- Identify the notation. In 1:30, the 30 is minutes. In 1.30 hours, the .30 is a fraction of an hour.
- For a decimal answer, use hours + minutes ÷ 60 + seconds ÷ 3,600. Keep the full value for later arithmetic and round only the display.
- To convert back, multiply the decimal by 3,600. If you need whole seconds, round once, then split the result into hours, minutes and seconds.
Worked examples
Convert to decimal
1:45 = 1 + 45 ÷ 60 = 1.75 hours.
Convert from decimal
1.30 hours = 1 hour + 0.30 × 60 minutes = 1 hour 18 minutes. By contrast, 1:30 is 1.50 hours.
Keep precision
Twenty minutes is exactly one third of an hour. Three entries of 20 minutes total 1 hour. Adding three displayed values of 0.33 would give 0.99 instead.
Quick reference
| Minutes | Decimal hours |
|---|---|
| 6 | 0.10 |
| 12 | 0.20 |
| 15 | 0.25 |
| 18 | 0.30 |
| 20 | 0.333… |
| 30 | 0.50 |
| 45 | 0.75 |
| 60 | 1.00 |
What to check
If you need a timesheet total, add the underlying durations first and convert the total once. Check which format the destination expects before pasting.
Related guides
Sources
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