Capacity Calculations

Capacity calculations work out whether a set of files will fit on a device, or how many copies of a file a device can hold. The key is always to get every value into the same unit before you add, compare or divide.

Storage needed for a set of files

Convert each file size to a common unit, add them up, then compare the total with the device capacity, which you also convert to that unit.

For example, a console has 8 games of 3.5 GB and 12 updates of 250 MB. The games need 8 × 3.5 = 28 GB. The updates need 12 × 250 = 3,000 MB, which is 3 GB. The total is 28 + 3 = 31 GB. A console with 32 GB free can hold them, leaving 1 GB spare.

How many files fit on a device

Put the capacity and the size of one file into the same unit, divide the capacity by the file size, then round down. Rounding down matters because part of a file cannot be stored: the leftover space is too small for one more whole file, so rounding up would promise a file that does not fit.

For example, a camera memory card has 128 GB free. Each RAW photo is 24 MB. Change the capacity to 128,000 MB, then do 128,000 ÷ 24 = 5,333.33 (to two decimal places). Round down to 5,333 whole photos. The remaining 0.33 of a photo is not enough for another photo, so it is wasted space.

Show your working

Write each conversion and each step as you go, keeping the units next to the numbers. Marks are awarded for the method as well as the final answer, so a correct answer with no working can still lose marks, and clear steps can earn marks even if a slip changes the final number.