Numbers in Latin

Most cardinal numbers are indeclinable. Those that do decline are shown below with their endings (masculine, feminine and neuter nominative); they are regular plural -us, -a, -um adjectives, except for one, two and three.

All ordinal numbers decline as regular -us, -a, -um adjectives. Those ending in -ēsimus can alternatively be written -ēnsimus.

Likewise, all distributive numbers are regular plural -us, -a, -um adjectives. These are also used instead of cardinal numbers for nouns which are plural in form but singular in meaning (e.g., bīnae scōpae “two brooms”, novēna castra “nine camps”), except that one and three have different forms for this purpose.

Adverbial numbers, like all adverbs, are indeclinable. Those ending in -iēns can alternatively be written -iēs.

All multiplicative numbers are third-declension i-stem adjectives with one ending for all genders, and genitive -plicis (e.g., triplex, triplicis “threefold, triple”). From these can also be derived multiplicative adverbs ending in -pliciter (e.g., tripliciter “in three ways, triply”).

Compound Numbers

For compound numbers 21–27, 31–37 etc., and 98 and 99, combine the tens and the ones (e.g., vīgintī trēs “23”, quīnquāgēsimus prīmus “51st”, nōnāgiēns quater “94 times”), usually without et. Cardinal numbers sometimes occur with ones before tens and with et (e.g., septem et sexāgintā “67”).

Compound numbers 28, 38 etc. are normally formed like 18: add duodē- to the next higher multiple of ten (e.g., duodēquadrāgēsimus “38th”, duodēoctōgiēns “78 times”). Similarly, 29, 39 etc. are formed like 19, with the prefix ūndē- (e.g., ūndēsexāgintā “59”, ūndēnōnāgēnī “89 each”).16 This usually does not apply to 98 and 99, but duodēcentum and ūndēcentum are found occasionally.

For numbers 101–199, 201–299 etc., combine the hundreds and the remainder (e.g., centum duodēvīgintī “118”, ducentēsimus trīcēsimus tertius “233rd”, sescentiēns semel “601 times”).

Fractions

Use an ordinal number with the feminine word pars, partis (e.g., nōna pars “a ninth”, vīcēsima pars “a twentieth”). If the numerator is greater than one, use a cardinal number; pars may be left implied (e.g., duae quīntae partēs “two-fifths”, septem octāvae “seven-eighths”). “One-half” is dīmidium, -ī (n.), or occasionally sēmis, sēmissis (m.).

There are also special nouns for one-twelfth and multiples thereof:

¹⁄₁₂

uncia, -ae (f.)

⅙

sextāns, -antis (m.)

¼

quadrāns, -antis (m.)

⅓

triēns, -entis (m.)

⁵⁄₁₂

quīncunx, -uncis (m.)

½

sēmis, sēmissis (m.)

⁷⁄₁₂

septunx, -uncis (m.)

⅔

bēs, bessis (m.)

¾

dōdrāns, -antis (m.)

⅚

dextāns, -antis (m.)

¹¹⁄₁₂

deunx, -uncis (m.)