In the Excel date system, one day is equal to 1, so you can think of time as fractional values of 1, as shown in the table below:
This means if you have a decimal number for hours, you can simply divide by 24 to get the correct representation of hours in Excel. After dividing by 24, you can apply a time format of your choice, or use the result in a math operation with other dates or times.
In the example, since B10 contains 12 (representing 12 hours) the result is 12/24 = 0.5, since there are 12 hours in a half of day. Once a time format like h:mm has been applied, Excel will display 12:00.
Durations longer than 24 hours
To display hours that represent a duration longer than 24 hours, you'll need to adjust the number format. Just wrap the h in square brackets like so:
To display in minutes, you can do the same thing with m:
The brackets tell Excel the time is a duration, and not a time of day. This article explains number formats in more detail.