doubledigit

Doubledigit, or two-digit, is a term used in mathematics to describe integers that have exactly two digits when written in decimal notation. In base-10, two-digit numbers span from 10 to 99 inclusive. In other bases, two-digit numbers represent any value from b to b^2 − 1, where b is the base.

Within decimal representations, a two-digit number consists of a tens digit (1–9) and a units digit (0–9). There are 9 possible tens digits and 10 possible units digits, yielding 9×10 = 90 distinct two-digit numbers. The sequence begins at 10 and ends at 99, forming a contiguous block of integers.

Two-digit numbers appear in everyday contexts such as ages, prices, and years. They also feature in educational tasks that involve place value, arithmetic, and digit analysis. In fixed-width formatting, leading zeros may be added to display a two-digit field, for example 03, but in standard notation a two-digit number does not include a leading zero.

See also: single-digit numbers, three-digit numbers, base-n numeral systems.