Expressing fractions in Spanish

Be careful not to mix up fractions (to describe a part of a whole: half, third, fourth...) and ordinal numbers (to describe an order/rank: 1st, 2nd, 3rd, 4th...).

For ordinal numbers, see Forming ordinal numbers (1st, 2nd, 10th...)

Look at these examples of fractions:

un tercioa third

un cuartoa quarter

dos quintostwo fifths

To express fractions in Spanish, you usually use both cardinal (un/dos/tres...) and ordinal numbers (cuarto/quinto...) the same way as in English (one fifth, two thirds...).

Note also that just like in English, the second number is plural if the first is. (dos quintos)


Half and Double

To say half and double we normally use the definite articles el and la.

La mitadHalf

El dobleDouble

Have a look at these examples to see fractions in context:

Me he comido dos tercios de la pizza.I had two thirds of the pizza.

Un cuarto de la población votó en contra.A quarter of the population voted against.

Puse solo la mitad de la harina en el bol.I only put half the (quantity of) flour in the bowl.

Ella tiene el doble de hermanos que él.She has twice as many siblings as he does.

Notice how, as we generally talk about a fraction "of" a whole, you will usually find "de" after the fraction.
 
Bear in mind that to say "half" [of something] you can also use "medio/media".

He cortado medio melón para nuestra cena.I cut half a melon for our dinner.

He cortado media sandía para nuestra cena.I cut half a watermelon for our dinner.

Notice how we use medio when we refer to a masculine noun (e.g., melón) and media when we refer to a feminine noun (e.g., sandía). It is only possible to use medio/a with singular nouns, not plural nouns:
"Medio pueblo salió a la calle a celebrar la fiesta."
"La mitad del pueblo salió a la calle a celebrar la fiesta."
"La mitad de los jóvenes salió a la calle a celebrar la fiesta."
"Medio/Medios jóvenes salieron a la calle a celebrar la fiesta."
Also notice above how medio/a are not followed by either "de" or "el/la".
 
Here is a list of fractions from half to a tenth:
 
1/2    la mitad [de] - medio/-a
1/3    un tercio [de]
1/4    un cuarto [de]
1/5    un quinto [de]
1/6    un sexto [de]
1/7    un séptimo [de]
1/8    un octavo [de]
1/9    un noveno [de]
1/10  un décimo [de]
 
 Here are more examples of fractions:

tres cuartosthree quarters

dos décimostwo tenths

tres octavosthree eighths

un séptimoone seventh

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Examples and resources

Me he comido dos tercios de la pizza.I had two thirds of the pizza.
un cuartoa quarter
He cortado media sandía para nuestra cena.I cut half a watermelon for our dinner.
Un cuarto de la población votó en contra.A quarter of the population voted against.
un séptimoone seventh
un tercioa third
He cortado medio melón para nuestra cena.I cut half a melon for our dinner.
El dobleDouble
tres octavosthree eighths
Ella tiene el doble de hermanos que él.She has twice as many siblings as he does.
La mitadHalf
dos décimostwo tenths
Puse solo la mitad de la harina en el bol.I only put half the (quantity of) flour in the bowl.
dos quintostwo fifths
tres cuartosthree quarters
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