Comparatives and Superlatives in Spanish

Comparatives of Inequality

To compare a feature of two unequal things or actions we use "more than" or "less than" in English. In Spanish we use "más que" or "menos que". The structure is as follow:

Subject (thing 1) + verb + comparator (más/menos) + adjective or adverb + the word "que" + noun (thing 2):

El perro de Alicia es más grande que el perro de Ana. (Alicia's dog is bigger than Ana's dog.)
Este vestido es menos lindo que el anterior. (This dress is less beautiful than the previous one.)
Alicia es más estudiosa que su hermana. (Alice is more diligent than her sister.)

With an adverb:
La mujer corre más rápidamente que el hombre (The woman runs faster than the man)

Comparatives of Similarity

In English, we use "as" twice in a sentence to compare two things that are similar, for example: "John's car is as big as Mary's." In Spanish, we use "tan" as equivalent for the first "as" and "como" for the second: "El coche de John es tan grande como el de Mary".

Another example:

Pedro es tan hábil como José (Pedro is as skilled as José).
Este pescado es tan sabroso como el tuyo (This fish is as tasty as yours).

Superlatives

The biggest, the most beautiful, etc... This means comparing a feature of a thing or an action to all the rest. In English we use "the most" or "the least." In Spanish we use "el/la/los/las más" or "el/la/los/las menos". The structure is as follows:

Subject + verb + article (el/la/los/las) + comparator (más/menos) + adjective or adverb + the word "de" + group:

Eduardo es el más bajo de la clase (Eduardo is the shortest of the class).
Teresa es la más bonita de las hermanas (Teresa is the most beautiful of the sisters).

Exceptions:
Like in English, where we say "good", "better", "the best" (and not "gooder" or "more good"), there are also exceptions in Spanish:

bueno (good) → mejor (better) → el mejor (the best)
malo (bad) → peor (worse) → el peor (the wort)

For age comparison:
joven (young) → menor (younger) → el menor (the youngest)
viejo (old) → mayor (older) → el mayor (the oldest)

For size comparison:
grande (big) → mayor (bigger) → el mayor (the biggest)
pequeño (small) → menor (smaller) → el menor (the smallest)

Examples:
Por su edad, Juan es el mayor de los primos. (Because of his age, Juan is the oldest of all cousins.)
Marta es menor que Florencia: nació después (Marta is younger than Florence: she was born later)
Esta película es la peor que he visto. (This movie is the worst I have seen.)
Sus excusas son cada vez peores (His excuses become worse every time.)

Please also note that "mejor", "peor", "mayor" and "menor" agree with the number of the subject, but not with the gender.