Let's say you want to find out how many hours there are in 5.5 days, or how many days there are in 3.45 years, or how precisely how many months will pass between a beginning date and an ending date.
There are several ways to convert time units.
Convert between time units
To convert from one time unit to another, use the CONVERT function.
Note: For conversions that involve a year, consider that a year is 365.25 days.
Convert a standard time format to a decimal number
To convert from hours : minutes : seconds format, use the INT function.
Convert from a decimal to the standard time format
To convert from decimal to hours : minutes : seconds format, use the divisor operator (/) together with the TEXT function.
Note: You can also apply the time format without using the TEXT function to specify the format. To view the number as a time: select the cell and, on the Home tab—in the Number group—click the arrow next to the Number Format box. Then click More Number Formats, click Custom in the Category list, and then click a custom format in the Type box. Keep in mind: if you use both a format applied with the TEXT function and number format, the TEXT function takes precedence.