You are already aware that the Spanish for one hundred is cien or ciento.

So, when do you use cien and when should you use ciento?

When there is exactly one hundred of something and the number is used with the noun, you use the shortened form cien, whether that noun is masculine or feminine. For example:

• cien libros - one hundred books
• cien plumas - one hundred pens

When you want to form numbers with 100, you would use ciento. For example:

101 - ciento uno (100/ciento + 1/uno = ciento uno)

114 - ciento catorce (100/ciento + 14/catorce = ciento catorce)

127 - ciento veintisiete (ciento + veintisiete = ciento veintisiete)

165 - ciento sesenta y cinco (ciento + sesenta y cinco = ciento sesenta y cinco)

Observe that "y" is NOT used to separate hundreds from tens and only used in numbers 131-199 (also 231-299, 331-399, etc).

In other words:

103 - ciento tres NOT ciento y tres

199 - ciento noventa y nueve NOT ciento y noventa y nueve

To count up in hundreds, the plural form of ciento is used - cientos - along with the appropriate number, and it is written as one word.

So, counting up in hundreds as far as a thousand, the Spanish numbers would be:

200 - doscientos        600 - seiscientos
300 - trescientos       700 - setecientos
400 - cuatrocientos     800 - ochocientos
500 - quinientos        900 - novecientos

Observe the slight irregularities in quinientos, setecientos and novecientos.

The Spanish numbers 200, 300, 400 etc have masculine and feminine forms. For example:

doscientos libros - 200 books (masculine noun)
doscientas plumas - 200 pens (feminine noun)

Using the Spanish numbers you have learnt so far and applying the relevant rules, here are examples of a few numbers between one hundred and a thousand.

153 - ciento cincuenta y tres     777 - setecientos setenta y siete
325 - trescientos veinticinco     802 - ochocientos dos 
513 - quinientos trece            948 - novecientos cuarenta y ocho

The Spanish for a thousand is, simply, mil, and this form is used when counting with other numbers.

However, should you wish to say "thousands of books", you would use the plural - "miles de libros".

Examples of some Spanish numbers using mil are:

mil - 1,000
diez mil - 10,000
cien mil - 100,000

mil trescientos dieciséis - 1,316
doce mil ochocientos cincuenta y cinco - 12,855
trescientos sesenta y dos mil ciento veintiuno - 362,121

The Spanish for a million is un millón.

Notice that, unlike the Spanish for a thousand, you need to include the un.

The same rule applies for the Spanish number for a billion - un billón. You have to include the un.

To make the plural of millón or billón, you just add -es and remove the accent.

Examples of these higher Spanish numbers would be:

dos millones cuatrocientos cincuenta y siete mil veintidos - 2,457,022

cinco millones trescientos ochenta y dos mil trescientos sesenta y ocho - 5,382,368