Digit One

The Digit One at U+0031 is the Basic Latin numeral used to write the number one in ordinary text, data, and notation. It is the ASCII digit for one and forms part of the decimal digits used in English and many other languages that use Western-style numerals. In everyday writing, it marks counts, quantities, dates, times, addresses, page numbers, rankings, and identifiers: 1 item, January 1, 1:30, Route 1, or Chapter 1. In mathematics and science, 1 represents the multiplicative identity, a unit amount, the exponent in x¹-style notation when superscripted by formatting, and values such as probability 1 for certainty. In computing and electronics, 1 is central in binary notation, Boolean values, bit fields, permissions, version numbers, and data entry, where it often means “on,” “true,” or an enabled state. It can be confused visually with lowercase l or uppercase I in some fonts, so technical identifiers often avoid mixing those characters when readability matters.