Expressing large numbers: hundreds, thousands, millions and billions

The way Spanish express "a hundred [things]", "a thousand [things]", "a million [things]" or "a billion [things]"  is slightly different to how this is expressed in English.

Let's see some examples:

One hundred/one thousand

Look at how the words "cien" and "mil" do not change when applied to masculine and feminine nouns: they are invariable. Also, notice how in Spanish there is no indefinite article "un" which is present in English. This is a very common mistake.

It'd be incorrect to say:

One million/one billion

Here, the words "millón" and "billón" don't change either when referring to masculine or feminine nouns, they too are invariable. However, we need:

• "un" before the number
• "de" before the noun

A common mistake for English speakers is to omit the "de" as it is not required in English. This is incorrect:

  

Hundreds/Thousands/Millions/Billions of [noun]

As you can see, there is only one form for both masculine and feminine plural.

Remember:

See also Using numbers + nouns

Important: about English billion and Spanish billón  

In Spanish, "un billón" refers to "un millón de millones" (a million million) while "a billion" in modern English refers to "a thousand million".

Note that previously in the UK a billion was "a million million" (just like  "un billón" in Spanish). Modern English texts do not use this system (the UK government adopted the newer system in 1974) and so it is not included in the table below. 

* In Spanish, the thousand separator is usually represented by a full stop/period, e.g. 1,000,000 = 1.000.000

** mil millones is used far more frequently that un millardo