Digit

A digit is a single written symbol used to construct numbers. The standard global system contains ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. When these symbols are arranged in sequence, they form a number; for example, 187 consists of three digits.

A crucial distinction exists between a digit and a number. A digit is the written symbol, whereas a number is the quantity that the symbol represents. The same number can be written using different digits—such as 12 (base 10), XII (Roman), or 1100 (binary)—while the numerical value remains the same.

Place value and positional notation

The modern system is positional: the value of a digit depends on its position. The number 187 means 1×100 + 8×10 + 7×1. Because the system uses base 10, each position to the left is worth ten times more. The system requires a dedicated symbol for zero, which marks an empty position, as in 105.

Other bases

The number of digits required depends on the base. Binary (base 2) uses only 0 and 1, and is the system computers use. Octal (base 8) uses 0–7. Hexadecimal (base 16) adds the letters A–F to provide sixteen distinct symbols. Ancient Babylonian systems used base 60, traces of which remain in the division of hours and degrees.

History and variant forms

The digits 0–9 now used worldwide are known as Hindu-Arabic numerals. They originated in Indian counting systems and reached Europe through the works of Arabic-writing mathematicians. To this day, written forms vary: Eastern Arabic digits (٠١٢٣٤٥٦٧٨٩) are still used in some Arabic and Persian texts.

Some systems are not positional. Roman numerals (I, V, X, L, C, D, M) rely on addition and subtraction of symbols, which made multiplication and division more difficult. Positional and zero-based systems simplified both hand calculation and machine computation.