0 to 9 refers to the set of ten single-digit symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) used as the basic building blocks of the decimal (base-10) positional numeral system. These symbols are known as numerical digits (from the Latin digiti, meaning "fingers"). The decimal system requires exactly ten distinct digits because its base is 10.
In positional notation, each digit's value depends on its position within a numeral. A digit placed in the rightmost "units" position represents its face value (0 through 9); digits to the left represent multiples of increasing powers of 10 (tens, hundreds, thousands, etc.), and digits to the right of a decimal separator represent fractions (tenths, hundredths, etc.). For example, in the numeral 345, the digit "3" represents 3 × 10² = 300, "4" represents 4 × 10¹ = 40, and "5" represents 5 × 10⁰ = 5.
The digits 0 to 9 are known as Hindu–Arabic numerals, originating from the Indian subcontinent by the 7th century CE. The digit zero (0) was first used in India around the 7th century by the mathematician Brahmagupta, though its first widely acknowledged use dates to 876 CE. The system was transmitted to the Islamic world and then to Europe, popularized by Fibonacci's Liber Abaci (1202). It replaced Roman numerals in common European use by the 16th century.
The 10 digits (0–9) are the foundation of the most widely used numeral system in the world. Different cultures represent the same numeric values with distinct glyphs—for instance, Eastern Arabic (٠١٢٣٤٥٦٧٨٩), Devanagari (०१२३४५६७८९), Chinese (〇一二三四五六七八九), and many others.
In computer science, the decimal digits 0–9 are also used within hexadecimal notation (0–9 plus A–F), while binary uses only the digits 0 and 1. The mathematical concept of digital root and casting out nines are operations derived from summing the digits 0–9 within larger numbers.
