Cardinal numbers answer “how many?”; ordinal numbers answer “which position in an ordered series?” Esperanto builds an ordinal by adding the adjective ending -a to a number: unu → unua, du → dua, dek → deka. Because the result is an adjective, it agrees in number and case just like any other adjective.
From quantity to position
The contrast is regular and meaningful:
| Cardinal | Ordinal | Meaning |
|---|---|---|
| unu | unua | one → first |
| du | dua | two → second |
| tri | tria | three → third |
| dek | deka | ten → tenth |
| cent | centa | one hundred → hundredth |
English has irregular forms such as “first,” “second,” and “third.” Esperanto has no comparable list to memorize: the same -a operation works from the start.
Tio estas mia unua tago en la nova laborejo.
This is my first day at the new workplace.
La dua buso iras rekte al la flughaveno.
The second bus goes directly to the airport.
Nia teamo finis la konkurson en la tria loko.
Our team finished the competition in third place.
A cardinal before a noun gives a quantity; an ordinal identifies a position:
Mi mendis tri kafojn.
I ordered three coffees.
Mi ne mendis la trian kafon; ĝi estis por mia kolego.
I did not order the third coffee; it was for my colleague.
Multiword ordinals
Build the cardinal first, in its normal order, and add -a only at the end:
| Number | Cardinal | Ordinal |
|---|---|---|
| 21 | dudek unu | dudek unua / dudek-unua |
| 47 | kvardek sep | kvardek sepa / kvardek-sepa |
| 132 | cent tridek du | cent tridek dua / cent-tridek-dua |
| 2026 | du mil dudek ses | du mil dudek sesa / du-mil-dudek-sesa |
Both spaced and compounded spellings are foundationally regular. In the compounded version, hyphens at the original word boundaries make a long form readable. A completely closed form such as dumildudeksesa is theoretically analyzable but needlessly opaque; du-mil-dudek-sesa or the spaced du mil dudek sesa is clearer.
Ŝi loĝas en la dudek-unua etaĝo.
She lives on the twenty-first floor.
Ĉu la centa gasto ricevos specialan donacon?
Will the hundredth guest receive a special gift?
Do not add -a to every component. Dudeka unua does not transparently build “twenty-first” from the cardinal dudek unu. Preserve the whole cardinal structure and convert it once at the end.
Ordinals behave like adjectives
An ordinal receives -j when it modifies a plural noun and -n when its phrase requires the accusative:
La unuaj tri ĉapitroj estas sufiĉe mallongaj.
The first three chapters are fairly short.
Mi legis la unuajn tri ĉapitrojn hieraŭ vespere.
I read the first three chapters last night.
In the second sentence, unuajn agrees with plural accusative ĉapitrojn. The cardinal tri remains invariant. This is a key difference between the derived adjective and the bare cardinal.
Put the ordinal before a following cardinal when you mean the first, next, or last members of one set: la unuaj dek paĝoj “the first ten pages.” The sequence la dek unuaj paĝoj can momentarily look like la dek-unuaj paĝoj, “the eleventh pages.” Clear ordering prevents that processing problem.
An ordinal can stand without an overt noun when the noun is recoverable. Its endings still reflect that noun:
El la tri proponoj, ni elektis la duan.
Of the three proposals, we chose the second one.
Duan is accusative because the understood phrase la duan proponon is the object of elektis.
Position versus an identifying number
Not every number attached to an object is ordinal. Room, bus, route, page, and model numbers often function as labels rather than rankings:
La kunveno okazos en ĉambro dudek unu.
The meeting will take place in room 21.
La dudek-unua ĉambro en la koridoro estas nun riparata.
The twenty-first room in the corridor is now being renovated.
Ĉambro dudek unu names the room by its assigned number. La dudek-unua ĉambro locates a room by counting its position. Both are correct, but they answer different questions.
In (formal) lists and technical documents, a label with numero is maximally explicit: artikolo numero 12, buso numero 4. An ordinal is better when actual order matters: la dek-dua artikolo de la kontrakto.
Dates
Esperanto normally expresses the day of the month as an ordinal, followed by de + month:
Morgaŭ estos la dudek-naŭa de Septembro.
Tomorrow will be the twenty-ninth of September.
The understood noun is tago. When the date is a time adjunct without a preposition, it commonly receives accusative -n:
La vespera kurso rekomenciĝos la trian de Oktobro.
The evening course will resume on the third of October.
English date conventions vary by country and can place the month first. In Esperanto words, the safe international order is day, then month: la tria de Oktobro, not a literal transfer of “October third.” This guide follows PMEG’s recommendation to treat month names as capitalized proper names. Lowercase oktobro is also widespread in contemporary texts; that orthographic variation does not change the date syntax.
Years are normally written in digits and can be read as cardinals with an understood la jaro: en la jaro du mil dudek ses. An ordinal reading such as la du-mil-dudek-sesa jaro is grammatical and historically attested, but the simple cardinal year is common in contemporary neutral usage. The dates and years page covers complete formats and regional ambiguity in all-numeric dates.
Clock hours and numbered units
The named clock hour is ordinal because it identifies a position in the daily cycle:
La filmo komenciĝos je la sepa kaj duono.
The film will begin at half past seven.
— Je kioma horo ni foriru? — Je la sesa, por eviti la trafikon.
— At what time should we leave? — At six, to avoid the traffic.
The question je kioma horo? asks for the numbered hour. By contrast, elapsed duration is cardinal: La filmo daŭras du horojn. The accusative on horojn marks measured extent; adding an ordinal does not express duration.
The same distinction applies to distance and stages:
Ni ripozis post la tria kilometro.
We rested after the third kilometer.
Ni marŝis tri kilometrojn antaŭ la matenmanĝo.
We walked three kilometers before breakfast.
The first identifies a point in a sequence. The second measures the length of the walk and therefore uses a plural noun in the accusative.
Writing ordinals with digits
In compact schedules and lists, a digit plus a hyphenated adjective ending is common: 1-a, 2-a, 21-a. Agreement endings replace or extend the basic form as normal: la 1-aj tri tagoj, mi elektis la 2-an. In running prose, writing short ordinals as words is usually more readable.
La 4-a kunsido komenciĝos je la 9-a.
The fourth session will begin at nine o'clock.
Do not copy English suffixes -st, -nd, -rd, or -th into Esperanto. The Esperanto ending is consistently -a, with -j and -n added when grammar requires them.
Common Mistakes
Copying English irregular ordinal forms
❌ Tio estas mia sekonda vizito al la urbo.
Incorrect for ‘second visit’ — sekundo is a unit of time, not the ordinal of du.
✅ Tio estas mia dua vizito al la urbo.
This is my second visit to the city.
Adding -a to every part
❌ Ŝi festis sian dudekan unuan naskiĝtagon.
Incorrect formation for twenty-first.
✅ Ŝi festis sian dudek-unuan naskiĝtagon.
She celebrated her twenty-first birthday.
Forgetting adjective agreement
❌ Mi legis la unua tri ĉapitrojn.
Incorrect — the ordinal modifies plural accusative ĉapitrojn.
✅ Mi legis la unuajn tri ĉapitrojn.
I read the first three chapters.
Copying English month-first date order
❌ La kunveno estos Oktobro tria.
Incorrect — a neutral Esperanto date uses an ordinal day followed by de plus the month.
✅ La kunveno estos la trian de Oktobro.
The meeting will be on the third of October.
Using an ordinal for measured distance
❌ Ni marŝis triajn kilometrojn.
Incorrect — this attempts to measure distance with an ordinal.
✅ Ni marŝis tri kilometrojn.
We walked three kilometers.
Key Takeaways
Add -a once, at the end of a cardinal structure, to express position. The resulting ordinal is an adjective and therefore takes -j and -n when its noun does. Distinguish genuine position from a mere number label, use ordinal days in dates and ordinal clock hours, and keep cardinal forms for quantities and measured extents.
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Start learning Esperanto →Related Topics
- Cardinal NumbersA1 — Use Esperanto cardinal numbers to count, quantify noun phrases, identify items, and read basic dates, times, measurements, and decimal notation.
- Building Large NumbersA1 — Build and use thousands, millions, and larger Esperanto numbers with correct spacing, noun behavior, scale values, and case marking.
- Numbers as Nouns, Adjectives, and AdverbsB2 — Change Esperanto number words into nouns, adjectives, and adverbs while preserving the distinction between quantity, order, and manner.
- Telling Clock TimeA1 — Ask and tell the time in Esperanto with ordinal hours, cardinal minutes, fractions, day-part expressions, and the correct time prepositions.
- Dates and YearsA2 — Form, inflect, write, and read Esperanto calendar dates and years without importing ambiguous English date order.
- Nouns after NumbersB1 — Use singular and plural nouns, adjective agreement, the accusative, and da correctly after Esperanto numbers.