16:21 = 16.3500 decimal hours. That's 981 minutes total, or 58,860 seconds. Decimal hours are used in payroll, billing, and timesheet systems because they use base-10 math.
Common HH:MM → decimal conversions
| HH:MM | Decimal hours | Decimal minutes |
|---|---|---|
| 0:15 | 0.25 | 15 |
| 0:30 | 0.50 | 30 |
| 0:45 | 0.75 | 45 |
| 1:00 | 1.00 | 60 |
| 1:15 | 1.25 | 75 |
| 1:30 | 1.50 | 90 |
| 1:45 | 1.75 | 105 |
| 2:00 | 2.00 | 120 |
| 8:00 | 8.00 | 480 |
| 8:30 | 8.50 | 510 |
| 8:45 | 8.75 | 525 |
💡 Did you know? Decimal time was proposed during the French Revolution (1793) as part of the metric system. The "decimal day" was 10 hours, each hour 100 minutes, each minute 100 seconds. It didn't catch on, but decimal hours survive in payroll and project management.
Frequently Asked Questions
16:21 = 16.3500 decimal hours. To convert: hours + (minutes ÷ 60) = 16 + (21 ÷ 60) = 16.3500.
1:30 = 1 + (30 ÷ 60) = 1 + 0.5 = 1.5 decimal hours. A common mistake is reading "1.5" as "1 hour 50 minutes" — it's actually 1 hour 30 minutes.
8:45 = 8 + (45 ÷ 60) = 8 + 0.75 = 8.75 decimal hours. 45 minutes is ¾ of an hour.
0:15 = 0 + (15 ÷ 60) = 0.25 decimal hours. 15 minutes is a quarter hour.
In Excel: =A1*24 (where A1 is a time value formatted as HH:MM). The result is decimal hours. To convert to decimal minutes: =A1*1440.
Many payroll and billing systems use decimal hours because they're easier to compute (no base-60 math). A worker who logs 7.75 hours gets paid the same as one who logs 7:45, but payroll math is simpler with decimals.
Hours = floor(decimal). Minutes = round((decimal - hours) × 60). So 8.75 → 8 hours + (0.75 × 60) = 8 hours + 45 minutes = 8:45. In Excel: =INT(A1) & ":" & TEXT((A1-INT(A1))*60, "00").
7.5 hours = 7 hours + (0.5 × 60) minutes = 7:30. Multiply the decimal part by 60 to get minutes.
