Latin numbers are usually adjectives. When there are three forms, the Latin number has a masculine, feminine, and neuter form, in that order. The numbers follow the appropriate declension rules. Note that there is no singular form for most of the numbers and no plural form for the number 1.
Here are the cardinal numbers, the "one", "two", "three", etc. of Latin. For the "first", "second", "third", etc., see the Latin Ordinal Numbers.
1 - unus, una, unum
2 - duo, duae, duo
3 - tres, tres, tria
4 - quattuor
5 - quinque
6 - sex
7 - septem
8 - octo
9 - novem
10 - decem
11 - undecim
12 - duodecim
13 - tredecim
14 - quattuordecim
15 - quindecim
16 - sedecim
17 - septendecim
18 - duodeviginti
19 - undeviginti
20 - viginti
21 - viginti unus
30 - triginta
40 - quadraginta
50 - quinquaginta
60 - sexaginta
70 - septuaginta
80 - octoginta
90 - nonaginta
100 - centum
200 - ducenti, ducentae, ducenta
300 - trecenti, trecentae, trecenta
400 - quadrigenti, quadrigentae, quadrigenta(*)
500 - quingenti, quingentae, quingenta
600 - sescenti, sescentae, sescenta
700 - septingenti, septingentae, septingenta
800 - octingenti, octingentae, octingenta
900 - nongenti, nongentae, nongenta
1000 - mille
2000 - duo milia
Take the Cardinal Numbers Quiz
See Latin adjectives for information about using the correct form of a number/adjective, and Latin Gender for the 3 genders. Also see: Roman Numerals, Comparison of Italian and Latin Numbers, and Roman Fractions
(*)I don't know if this tip will help you, but it does help me when I'm looking at the spelling and trying to decide whether a part of the numeral is a multiple of 10 or "20" (viginti) or "100" (centum).
septuaginta vs. septingentiVisually they look similar and I can't easily distinguish the sounds by pronouncing them aloud to myself.
- The initial sound of centum, /k/, is a voiceless velar. /g/ is the voiced velar. Say: CENTUM and then say GENTUM. They're pretty close. Whether you pronounce the sound voiced or unvoiced depends on what precedes it. So, I don't look at whether there is a "c" or a "g".
- Note that in the compounds there is often a condensed version of viginti (gint-), so you can't count on the "vi" to tell you the answer.
- In the compound numbers, I look beyond the c/g to the vowel. If it's an "i", as in "gint", it's 20 (really, some multiple of ten), if it's an "e", as in "gent" or "cent", it's a multiple of 100.
