Cardinal Numbers

Cardinal numbers answer kiom? “how many/how much?” Esperanto builds them from a small set of invariant number particles, and their structure is highly regular. The main challenge for English speakers is not memorizing irregular forms, but putting spaces in the right places and leaving the cardinal itself unchanged while the noun shows plural and case.

The basic cardinal words

These thirteen forms—nul, unu through naŭ, dek, cent, and mil—are the basic number particles. They are register-neutral and do not take -j or -n when used as ordinary cardinals.

The nouns tell you the grammatical role: fratinojn and lokojn are plural direct objects. The numbers du and tri stay unchanged.

Building numbers below one thousand

For 11–19, say dek plus the unit as separate words: dek unu, dek du, dek naŭ. For exact tens, attach the multiplier directly to dek: dudek, tridek, kvardek, and so on. Then add any unit as a separate word.

Multiplication by dek or cent is written as one word: sesdek, okcent. Addition is written with spaces: sesdek kvin, okcent du. There is no word corresponding to English “and” inside a cardinal number.

For thousands and larger values, continue on building large numbers.

Cardinals inside a noun phrase

An ordinary cardinal directly modifies a count noun. With any exact number greater than one, the noun is plural:

If the noun phrase is a direct object, the noun and its agreeing adjective take accusative -n; the number does not:

English marks plural only once in “two cups”; Esperanto still requires plural -j on the noun and agreeing adjective because the number does not replace ordinary agreement. So tri ruĝaj pomoj is nominative and tri ruĝajn pomojn is accusative.

The basic cardinals can also stand alone when the noun is recoverable:

With nul, a following count noun is normally plural: nul gradoj, nul poentoj, nul mesaĝoj. Outside measurements and scores, neniu often sounds more natural when the intended meaning is “not any” rather than the numerical value zero:

The noun nulo names the digit or number zero. In decimal readings, both nul and nulo are established before komo.

Counted things and measured substances

A number directly counts units: tri boteloj, du kilogramoj, kvin horoj. When a unit measures a substance, connect that substance with da:

Here the direct objects are the units litrojn and kilogramojn; da lakto and da terpomoj identify what is measured. Do not put da between an ordinary cardinal and the item it directly counts: tri terpomoj, not tri da terpomoj.

A bare measurement can describe extent. In the common no-preposition construction, the measured phrase takes accusative -n:

The number remains invariant; metrojn and minutojn carry the endings. This use is developed on the page about distance and extent.

Cardinals, ordinals, and fractions

A cardinal gives a quantity: tri ĉambroj “three rooms.” Add adjective -a to express order: tria ĉambro “third room.” Multiword ordinals put the ending at the end and may be written with spaces or, for clarity, joined with hyphens: dudek unua or dudek-unua “twenty-first.” Ordinals behave like adjectives and therefore can take -j and -n.

Fractions use -on-: duono “one half,” triono “one third,” kvarono “one quarter.” The denominator supplies the derived fraction word; the numerator is expressed separately when necessary: tri kvaronoj “three quarters.” These systems are regular extensions, covered fully under ordinal numbers and fractions.

Dates and clock time are not plain counting

The day of a month is ordinal because it identifies a position among the days: la dudek-oka de Septembro “the twenty-eighth of September.” The month follows de. A year is normally written in digits and may be read as a cardinal.

When the date tells when an event occurs, the omitted word tagon often leaves an accusative ordinal:

This day–month–year organization differs from normal U.S. English order. In international numeric writing, 2026-09-28 follows ISO year–month–day order and avoids the ambiguity of forms such as 9/10/2026.

Clock hours are also ordinal: Estas la tria “It is three o’clock.” Minutes are cardinal. For the time at which something happens, use je, not a bare accusative hour:

See telling clock time for alternative ways of saying quarter and half hours.

Digits and exact formatting

Esperanto uses the familiar digits 0–9. In careful international typography, group long integers with narrow spaces, not commas: 12 345 678. A comma marks decimals: 3,14, read tri komo unu kvar. Because national conventions differ, retain the written unit and use unambiguous spacing in data intended for an international audience.

Room, page, route, and model numbers can identify rather than count. Ĉambro 204 is read as a number label; it need not be the 204th room that physically exists:

Common Mistakes

Giving a cardinal plural or accusative endings

Leaving the counted noun singular

Joining additive parts

Copying English date order

Omitting accusative on a measured extent

Key Takeaways

Basic cardinal particles are invariant. Join a multiplier to dek or cent, but separate added components. Put plural and case endings on the noun and its adjectives, not on the cardinal. Distinguish counting from ordinals, dates, clock hours, labels, and measured extents; in international numeric text, use spaced digit groups, a decimal comma, and unambiguous date formats.