ciento

Ciento is a cardinal number in Spanish used to express the quantity 100 when it forms part of larger numbers. Its form derives from Latin centum. The word cien is used for exactly 100 or before a noun (such as cien años, cien libros), while ciento is used when 100 is followed by additional digits to form numbers from 101 to 199.

In practice, 101 is ciento uno, 110 is ciento diez, 150 is ciento cincuenta, and 199 is ciento noventa y nueve. This pattern continues only up to 199; once the hundred is reached or surpassed by larger counts, Spanish uses a different construction for the hundreds: doscientos, trescientos, cuatrocientos, quinientos, seiscientos, setecientos, ochocientos, and novecientos. For example, 215 is doscientos quince, and 348 is trescientos cuarenta y ocho.

Beyond 199, the numbers follow the regular hundreds system, with thousands and millions forming as in other contexts. The expression cien por ciento is a common fixed phrase meaning one hundred percent, used in contexts such as performance or completeness.

Etymologically, ciento reflects the same root as centum in Latin, with phonetic and orthographic evolution that yields cien for exact 100 and ciento for 101–199 in contemporary Spanish. The distinction between cien and ciento is a standard feature of Spanish number syntax and is widely observed in formal and informal usage.