There are a variety of number systems used throughout Focus. The two widely used in natural language are duodcimal, used in Commonthroat, and quadravigessimal, used in Outlander.

This difference exists due to the cultural divide between surface dwellers and spacers. Yinrih have six digits on each of their four paws, for a total of 24 digits. Yinrih are arboreal quadrupeds, so they have to stop and rear up on their hind feet when on level ground in order to use their forepaws, giving them twelve digits to count with. Spacers live in microgravity, allowing them to use all 24 digits to count. The Allied Worlds, where Commonthroat is spoken, contains a larger population of surface dwellers, while Moonlitter and Partisan Territory contain a large population of spacers, so Outlander, the local language, uses base 24.

Two specialized bases exist that are used in computing. Yinrih computers are based on balanced ternary. Balanced base 27 is used as a convenient shorthand for balanced ternary as hexadecimal is for binary on Earth.