How Small Is Smaller

This reading explains the units that measure the size of a file, from the smallest to the largest.

From Bits to Gigabytes

The smallest unit of digital storage in this reading is the bit. A byte is a group of 8 bits, and file sizes are usually counted in bytes or in larger units built from bytes. A kilobyte (KB) is 1,000 bytes, a megabyte (MB) is 1,000,000 bytes, and a gigabyte (GB) is 1,000,000,000 bytes. From the byte upward, each unit is therefore exactly 1,000 times larger than the unit before it. Some computer programs and operating systems count a kilobyte as 1,024 bytes instead, so two different devices can display slightly different numbers for the same file. The CompTIA Tech+ exam lists the bit, the byte, the KB and the GB among the storage units that it tests.

Measuring the Three Saves

Figure 1 shows one photograph saved three times at different quality settings, and each save produced a file of a different size. Save 1 is 686,688 bytes, which is between 686 KB and 687 KB and less than 1 MB. Save 2, at 190,572 bytes, falls between 190 KB and 191 KB, and save 3, at 85,533 bytes, falls between 85 KB and 86 KB. Measured in bits, save 3 is 684,264 bits, because each of its 85,533 bytes holds 8 bits.

Because save 3 is the smallest of the three files, a fixed amount of storage can hold more copies of it than of either of the others. One gigabyte holds 11,691 complete copies of save 3, with 33,697 bytes remaining, while the same gigabyte holds only 5,247 copies of save 2 and 1,456 copies of save 1. A phone with 64 GB of free space could therefore hold 748,249 copies of save 3, 335,831 copies of save 2 or 93,200 copies of save 1. The smaller file comes at a cost, however, because save 3 also preserved the least detail of the three photographs.

Sources: NIST, The Binary Prefixes (n.d.); Deutsch, RFC 1951 (1996); CompTIA, Tech+ Certification (2024); classroom data, Three JPEG Saves (2026).