1.  Portuguese adjectives ending with the masculine singular -o (e.g. novo = new, gordo = obese, rico = rich, alto = high/tall) can be changed to the feminine singular form by substituting the ending -o with an -a.

o homen rico (m; sing.) = the rich man
a mulher rica (f; sing.) = the rich woman

2.  Masculine singular adjectives ending with -e are most often unchanged in the feminine singular (e.g. forte =strong, grande = big, inteligente = intelligent, verde = green, etc).

o carro verde (m; sing.) = the green car
a bolsa verde (f; sing.) = the green purse

3.  Masculine singular adjectives ending with a consonant usually remain unchanged in the feminine singular. The exception is adjectives that indicate nationality and end with -es, -l and/or -or. In these cases, the feminine form is created by adding -a to the existing masculine form.

o céu azul (m; sing.) = the blue sky
a bolsa azul (f; sing.) = the blue purse
um carro inglês = the English car
a língua inglesa = the English language

4.  For adjectives ending with -ão, the final -o is dropped to create the feminine form.

o carro alemão = the German car
a cerveja alemã = the German beer

5.  For adjectives ending with -u, an -a is added to create the feminine form.

o arroz cru = the uncooked rice
a carne crua = the raw meat

6.  Adjectives ending with -eu, are changed to -éia to create the feminine form.

o clima europeu = the European climate
a cooperação européia = the European cooperation