Seven hours thirty minutes is not 7.30 hours. It is 7.5. That one slip is behind a lot of payroll errors, and it is easy to avoid once you see how the conversion works.
The formula
There are 60 minutes in an hour, not 100, so the minutes have to be divided by 60 before they can sit after a decimal point.
8 hours 20 minutes = 8 + (20 ÷ 60) = 8.33 hours
6 hours 45 minutes = 6 + (45 ÷ 60) = 6.75 hours
Minutes to decimal chart
| Minutes | Decimal | Minutes | Decimal | Minutes | Decimal |
|---|---|---|---|---|---|
| 1 | 0.02 | 21 | 0.35 | 41 | 0.68 |
| 3 | 0.05 | 24 | 0.40 | 42 | 0.70 |
| 5 | 0.08 | 25 | 0.42 | 45 | 0.75 |
| 6 | 0.10 | 27 | 0.45 | 48 | 0.80 |
| 10 | 0.17 | 30 | 0.50 | 50 | 0.83 |
| 12 | 0.20 | 33 | 0.55 | 54 | 0.90 |
| 15 | 0.25 | 35 | 0.58 | 55 | 0.92 |
| 18 | 0.30 | 36 | 0.60 | 57 | 0.95 |
| 20 | 0.33 | 40 | 0.67 | 60 | 1.00 |
The ones worth memorising are the quarter hours: 15 minutes is 0.25, 30 is 0.5 and 45 is 0.75. Every 6 minutes is one tenth of an hour.
What the mistake costs
An employee on $34 an hour works 7 hours 45 minutes. The correct pay is 7.75 × $34 = $263.50. Entered as 7.45, it comes out at $253.30, which is $10.20 short for one shift. Over a year of shifts that adds up, and underpayments have to be back-paid.
Going the other way
To turn decimal hours into hours and minutes, keep the whole number and multiply the decimal part by 60.
5.4 hours: 0.4 × 60 = 24, so 5 hours 24 minutes.
Adding up a week
Convert each day to decimal first, then add. Or add the hours and minutes separately and convert the total: 37 hours 150 minutes is 37 + 2.5 = 39.5 hours.
Skip the arithmetic: open the time to decimal calculator, then take the result to the pay calculator.