Seis vs. meia
In Portuguese, both seis and meia are used to represent the number 6. While seis is the standard counting number, meia is a widely used oral substitute, particularly in Brazil, derived from the phrase meia dúzia (half a dozen). Its primary purpose is to distinguish the sound of the word seis from the word três (three) when speaking.
Seis
A1This is the grammatically correct cardinal number for 6. You use seis for mathematics, counting quantities of objects, telling time, stating ages, and general usage.
Eu comprei seis maçãs no mercado.
(I bought six apples at the market.)
São seis horas da manhã.
(It is six o'clock in the morning.)
Três vezes dois é igual a seis.
(Three times two equals six.)
Meu filho tem seis anos de idade.
(My son is six years old.)
Meia
A1Literally meaning half (short for meia dúzia or half a dozen), this word replaces seis almost exclusively when reciting a sequence of digits. It is used in phone numbers, zip codes, and ID numbers to ensure the listener does not mishear seis as três (three).
O meu número é nove, oito, meia, zero.
(My number is nine, eight, six, zero.)
A senha do banco é meia, dois, meia.
(The bank password is six, two, six.)
Anote o código postal: um, três, meia, cinco.
(Write down the zip code: one, three, six, five.)
Ele mora no apartamento número meia um.
(He lives in apartment number six-one.)
Summary
Always use seis when counting items or doing math. Switch to meia only when dictating a string of digits—like a phone number—to avoid audio confusion between seis and três.