Decimal Hours Explained

A practical method

Decimal hours express part of an hour as a base-10 fraction, while clock time uses 60 minutes per hour. That is why 7 hours 30 minutes becomes 7.5 hours, but 7 hours 45 minutes becomes 7.75 rather than 7.45. Decimal hours are common in payroll, billing, time sheets, and project costing.

1. Separate complete hours and minutes: Keep the whole-hour value and convert only the remaining minutes.
2. Divide minutes by 60: Thirty minutes is 30 ÷ 60 = 0.5 hour; 15 minutes is 0.25 hour.
3. Add the values: Combine the whole hours with the fractional hour, then round only at the required final precision.
4. Convert back when needed: Multiply the decimal part by 60. For 8.35 hours, 0.35 × 60 = 21 minutes.

Worked example

A shift lasts 8 hours 17 minutes. Divide 17 by 60 to get 0.2833, then add 8 for 8.2833 hours. Rounded to two decimals, the result is 8.28 hours. Interpreting 8:17 as 8.17 would understate the time by more than six minutes.

Checks, edge cases, and common mistakes

• Do not place minutes after a decimal point without conversion.
• Apply the employer's stated rounding policy consistently and disclose it.
• Keep unrounded values during intermediate calculations to avoid cumulative error.
• Confirm whether a time sheet expects hundredths, tenths, or quarter-hour increments.