what is it?
Spanish has two number systems. Cardinal numbers (uno, dos, cien, doscientos…) express quantity — how many of something there are. Ordinal numbers (primero, segundo, tercero…) express position in a sequence — which place something occupies. Unlike English, several Spanish cardinals and all ordinals must agree in gender and number with the noun they modify.
when to use it
Counting nouns (cardinals): Use cardinals whenever you state a quantity: prices, ages, quantities of objects, phone numbers, years.
Gender-sensitive cardinals: uno and the hundreds forms -cientos / -cientas agree with the noun's gender. All other cardinals are invariable.
Ordering things (ordinals): Use ordinals primero–décimo for floors, rankings, chapters, and similar sequences. Beyond tenth, cardinals are commonly used instead (el piso once).
Shortened ordinals before masculine singular nouns: primero and tercero drop their final -o when placed directly before a masculine singular noun: el primer piso, el tercer día.
formation
Cardinals: uno and the hundreds
Only uno / una and the hundreds from 200 upward change for gender. In compound numbers, uno shortens to un before a masculine noun and to una before a feminine noun.
| number | masculine | feminine |
|---|---|---|
| 1 | un / uno | una |
| 21 | veintiún | veintiuna |
| 200 | doscientos | doscientas |
| 300 | trescientos | trescientas |
| 500 | quinientos | quinientas |
| 700 | setecientos | setecientas |
| 900 | novecientos | novecientas |
Ordinals: primero–décimo
Ordinals agree in gender and number with the noun. Primero and tercero shorten to primer and tercer immediately before a masculine singular noun.
| ordinal | masc. singular | fem. singular | masc. plural | fem. plural |
|---|---|---|---|---|
| 1st | primero (primer) | primera | primeros | primeras |
| 2nd | segundo | segunda | segundos | segundas |
| 3rd | tercero (tercer) | tercera | terceros | terceras |
| 4th | cuarto | cuarta | cuartos | cuartas |
| 5th | quinto | quinta | quintos | quintas |
| 6th | sexto | sexta | sextos | sextas |
| 7th | séptimo | séptima | séptimos | séptimas |
| 8th | octavo | octava | octavos | octavas |
| 9th | noveno | novena | novenos | novenas |
| 10th | décimo | décima | décimos | décimas |
The short forms primer and tercer are used only before a masculine singular noun. In all other positions the full forms primero and tercero are used: «el primero de mayo», «llegó el tercero».
examples in context
common pitfalls
Wrong gender on -cientos. The hundreds from 200 upward must match the noun's gender. Do not leave them in the masculine when the noun is feminine.
✗ *doscientos mujeres ✓ doscientas mujeres
Forgetting to shorten primero/tercero. Before a masculine singular noun, primero and tercero must drop the final -o.
✗ *el primero piso ✓ el primer piso
Using uno instead of un in compound numbers. In compound cardinals before a masculine noun, uno shortens to un (and takes a written accent in the compound veintiún).
✗ *veintiuno libros ✓ veintiún libros
Three sentences, graded here. Nothing is saved and no account is needed.
Mi clase de español es en el ___ piso del edificio. (7.º)
Fill in the blank with the correct ordinal number form indicated by the digit cue in parentheses.