A file size is the measure of space a file takes on a storage medium such as a computer hard drive. File sizes can be measured in bytes (B), kilobytes (KB), megabytes (MB), gigabytes (GB), terabytes (TB), and beyond. In the picture below of files listed in Windows Explorer, the size column is sorted to show the largest file first. As can be seen, the first file "family-safety.jpg" has a file size of 47 KB. The smallest file in this picture has a file size of 32 KB.