Numerals

Numerals are the words that express precise quantity or order. The Portuguese grammatical tradition recognises four classes: cardinals (quantity — um, dois, cem, “one, two, a hundred”), ordinals (rank in a series — primeiro, segundo, “first, second”), multiplicatives (how many times — dobro, triplo, “double, triple”) and fractionals (a part of a whole — meio, terço, “half, third”). A few numerals inflect for gender and number; most are invariable.

Cardinals

Cardinals name quantity. Almost all are invariable, but three groups inflect for gender: um/uma (“one”), dois/duas (“two”) and the hundreds from duzentos upward.

Among the tens, European Portuguese keeps the etymological a in dezasseis (16), dezassete (17) and dezanove (19) — a small detail that instantly sets the Lisbon norm apart from the Brazilian one. Compound forms are joined with e (“and”): vinte e um (21), cento e cinquenta e três (153).

Cem and cento; the milhão and the mil milhões

The form cem [sɐ̃j̃] is used before a noun or a larger numeral (cem casas “a hundred houses”, cem mil “a hundred thousand”); the form cento appears in compounds followed by units or tens (cento e um “a hundred and one”, cento e vinte “a hundred and twenty”). Mil (“thousand”) is invariable as a numeral (dois mil), but takes a plural when used as a noun (aos milhares “by the thousand”).

Milhão, bilião and trilião are, strictly, nouns: they pluralise (dois milhões) and require the preposition de before what is counted (um milhão de euros “a million euros”). Here lies a notable divergence between the norms: on the long scale used in Portugal, 10⁹ is mil milhões (“a thousand million”), and bilião is reserved for 10¹².

Ordinals

Ordinals mark position in a sequence and always agree in gender and number with their noun: a primeira fila (“the first row”), os primeiros lugares (“the first places”). From first to tenth they are inherited words; the tens, hundreds and thousands have learned, Latin-based forms.

Cardinal	Ordinal		Cardinal	Ordinal
1	primeiro		10	décimo
2	segundo		20	vigésimo
3	terceiro		30	trigésimo
4	quarto		40	quadragésimo
5	quinto		50	quinquagésimo
6	sexto		100	centésimo
7	sétimo		1000	milésimo
8	oitavo
9	nono

High ordinals are rare in speech: for monarchs, centuries and chapters the language often switches to the cardinal beyond a certain point (D. João VI, read sexto “the sixth”, but Luís XIV read catorze “the fourteenth”; o século XXI “the 21st century”, said vinte e um as readily as vigésimo primeiro).

Multiplicatives and fractionals

Multiplicatives express multiplication: dobro/duplo (“double”), triplo (“triple”), quádruplo, quíntuplo, sêxtuplo… They behave as nouns (o dobro do preço “twice the price”) or as adjectives (uma dose dupla “a double dose”).

Fractionals name the parts of a whole. In the denominator, from 2 to 10 the language uses the proper forms and the ordinals — meio “half”, terço “third”, quarto “quarter”, quinto… décimo — and from 11 upward the cardinal followed by avos.

Note the difference between meio (a numeral, variable: meia dúzia “half a dozen”, meio litro “half a litre”) and metade (a noun, “the half”). In telling the time, European usage says meio-dia e meia (“half past noon”), where meia agrees with the understood (hora).