The numbers in Esperanto

Cardinal numbers

• 0: nul.
• 1: unu.
• 2: du.
• 3: tri.
• 4: kvar.
• 5: kvin.
• 6: ses.
• 7: sep.
• 8: ok.
• 9: naŭ.
• 10: dek.
• 11: dek unu.
• 12: dek du.
• 20: dudek.
• 21: dudek unu.
• 100: cent.
• 1000: mil.

Let’s see some examples:

• -7890: minus sep mil okcent naŭdek.
• 1,621: unu komo sescent dudek unu.
• 1/2: duono.
• 56/99: kvindek ses naŭdekonoj.

Notice that fractions use the ending -ono only in the denominator. If the numerator is a one then it is omitted when reading it. When using them in sentences they usually describe some noun, like adjectives but unlike them, they don’t take any special ending:

• I have 20 fingers: Mi havas dudek fingrojn.
• 200 is too much: Ducent estas tro multe.

Ordinal numbers

Ordinal numbers are just the adjectival form of the cardinal numbers, so just add the -a ending. Also as adjectives, they take any ending and follow every rule of any other:

• First: Unua.
• Tenth: Deka.
• He is the 23rd in line: Li estas la dudek tria en vico.

Notes

• Esperanto is not that succinct with its rules on numbers, there are more relating to numbers in other usages https://lernu.net/en/gramatiko/nombraj_vortoj.