Spanish numbers 1 to 100, with a converter up to 999,999

Up to fifteen each number has its own word. From sixteen, numbers are built from ten or twenty plus a unit, and up to twenty-nine they are written as a single word: dieciséis, diecisiete, veintiuno, veintinueve. Four of them carry a written accent: dieciséis, veintidós, veintitrés, veintiséis.

The older three-word spellings (diez y seis, veinte y uno) are understood but no longer standard.

Thirty-one onwards is three words: tens, y, units. treinta y uno, cuarenta y dos, noventa y nueve. The y only ever joins tens to units. Hundreds attach directly: ciento treinta y uno, never ciento y treinta.

Exactly one hundred is cien, and so is a hundred of a bigger unit: cien mil. As soon as anything follows within the hundred it becomes ciento: ciento uno, ciento cincuenta. The other hundreds are one word ending in -cientos, three of them irregular: quinientos (500), setecientos (700), novecientos (900). They agree with a feminine noun: doscientas personas.

Counting, it is uno. In front of a masculine noun it drops the o: un libro, veintiún años, treinta y un días. Before a feminine noun it is una: una casa, veintiuna personas. The same happens in front of mil: veintiún mil.

One thousand is just mil, not un mil, and it does not pluralize when multiplied: dos mil, diez mil, novecientos mil. Spain writes the thousands separator as a dot (1.000) and the decimal as a comma; much of Latin America does the reverse.