How do I convert minutes to decimal hours?

Divide by 60. Thirty minutes is 30 ÷ 60 = 0.5 hours. Fifteen minutes is 0.25 hours. Forty-five minutes is 0.75 hours. The awkward ones are the ones that do not divide evenly: 20 minutes is 0.3333… hours, and 10 minutes is 0.1667 hours.

Why do timesheets use decimal hours?

Because arithmetic is simpler. Adding 1.75 + 2.5 gives 4.25 hours; adding 1:45 + 2:30 requires carrying 75 minutes into 1 hour and 15 minutes. Payroll multiplies hours by a rate, and that multiplication only works cleanly on a decimal.

Is there a difference between a second and a clock second?

For everyday purposes, no. The SI second is defined by a cesium atom, and a clock second is one-sixtieth of a minute. They agree to within a leap second every few years, and this calculator treats them as the same thing.

Time & dates

Time Calculator

Enter hours, minutes and seconds. The duration appears in every common unit.

The link carries your figures, so it reopens on exactly these numbers.

The formula

total seconds = hours × 3600 + minutes × 60 + seconds

total minutes = total seconds ÷ 60

decimal hours = total seconds ÷ 3600

milliseconds = total seconds × 1000

Worked example

2 hours, 30 minutes and 45 seconds

total seconds = 2 × 3600 + 30 × 60 + 45 = 9,045
total minutes = 9,045 ÷ 60 = 150.75
decimal hours = 9,045 ÷ 3600 = 2.5125
milliseconds = 9,045 × 1,000 = 9,045,000

Where this goes wrong

Decimal hours are not hours and minutes

2.5 hours is 2 hours and 30 minutes, not 2 hours and 50 minutes. Timesheets, billing software and payroll systems all use decimal hours, and misreading the decimal part as minutes is the single most common time-conversion mistake. The digits after the point are hundredths of an hour, not minutes out of sixty.

Questions

How do I convert minutes to decimal hours?: Divide by 60. Thirty minutes is 30 ÷ 60 = 0.5 hours. Fifteen minutes is 0.25 hours. Forty-five minutes is 0.75 hours. The awkward ones are the ones that do not divide evenly: 20 minutes is 0.3333… hours, and 10 minutes is 0.1667 hours.
Why do timesheets use decimal hours?: Because arithmetic is simpler. Adding 1.75 + 2.5 gives 4.25 hours; adding 1:45 + 2:30 requires carrying 75 minutes into 1 hour and 15 minutes. Payroll multiplies hours by a rate, and that multiplication only works cleanly on a decimal.
Is there a difference between a second and a clock second?: For everyday purposes, no. The SI second is defined by a cesium atom, and a clock second is one-sixtieth of a minute. They agree to within a leap second every few years, and this calculator treats them as the same thing.