Although mastering numbers in order is not a very difficult task, there is so much more to understanding numeric values in another language. Numbers are not read the same way when they are ordinal numbers or part of a whole as in a fraction. Here is how to use numbers in Spanish.
Spanish Ordinal Number Basics
So just as we learn that numbers one, two, and three, are read as first, second, and third when in a line, we must acquire the same knowledge in our second language.
In Spanish, each ordinal position has its own term.
Abbreviated Ordinal Numbers
Just as in English, these numbers can be abbreviated by using the numeral.
After tenth, the names for these places take on a different pattern. Most of the time you will just add –avo after the name for the number. For example, eleventh would be onceavo (once meaning 11), and twelfth would be doceavo (doce being 12), and so on.
Fractions tend to use the same –avo suffix to refer to the divisor as used in position words 11th and up after the basic fractions from ½ to 1/10th.
1/2 = la mitad
1/3 = un tercio
1/4 = un cuarto
1/5 = un quinto
1/6 = un sexto
1/7 = un séptimo
1/8 = un octavo
1/9 = un noveno
1/10 = un décimo
When more than one piece of the fraction is present, the top number is read as it would normally be read, and the bottom number would be read as the fractional number.
Consider these examples:
2/10 would be read as dos décimos
3/6 would be read as tres sextos
9/12 would be read as nueve doceavos
5/8 would be read as cinco octavos
Variations and Related Vocabulary
Some variations occur in special situations such as when referring to floors in a building. The first floor in the US is simply the first floor. In Spanish, the first floor does not exist. It is referred to as Planta Baja (ground floor) and abbreviated as PB in elevators. You might think this would be common sense, but I spent quite a while wondering why I could never get directly to the first floor of our office building.
Other related vocabulary words could be used when it comes to referring to the quantity of people. For example, a single/twin bed would be called cama sencilla (simple bed) and a double bed would be a cama doble. Twins themselves would be called cuates if they were not identical and gemelos if they are identical. Triplets are called triates.
Prefixes regarding numbers that are used in English such as bi- and tri- are used, but used less frequently in Spanish. Although you will see the words bilingue, and bicicleta, you would not use these in words like biweekly. Instead you would say cada dos semanas (or every two weeks), or if talking about payday, on the quincena (15th). Using these types of prefixes is not wrong or unheard of in Spanish, but it is typically better to stick with the most frequently used vocabulary of the speakers that surround you.