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The basic, “cardinal” numbers of Ido are:

un — one ok — eight
du — two non — nine
tri — three dek — ten
quar — four cent — hundred
kin — five mil — thousand
sis — six milion — million (106)
sep — seven miliard — billion (109)

These words are all roots, and are used without further modification before nouns to convey quantity:

tri saji three wisemen
sep nani seven dwarves
ok tre mikra rentiri eight tiny reindeer
non muzi nine muses

One can combine the roots by dropping their endings and inserting -a- for multiplication or e (as a separate word or not, with or without hyphens) for addition to produce numbers greater than ten:

Ci iras til dek-e-un. These go to eleven.
quaradek jorni, quaradek nokti forty days, forty nights
La Fola Okadek-e-ok The Crazy Eighty-Eight
Duamil-e-un: Kosmala odiseo Two Thousand One: A Space Odyssey
Vi mustos pagar a me ... MILION DOLLARS. Pardonez ... CENT E MILIARD DOLLARS! You’re going to have to pay me ... ONE MILLION DOLLARS. Sorry ... ONE HUNDRED BILLION DOLLARS!
nonacent e nonadek e nonamil e nonacent e nonadek e non boteli de biro an la muro nine hundred ninety-nine thousand nine hundred ninety-nine bottles of beer on the wall

As in English, one need not pronounce larger numbers in all their awkward fullness, but can break them down into smaller, more manageable chunks:

non-non-non-mil, non-non-non boteli de biro an la muro nine ninety-nine thousand nine ninety-nine bottles of beer on the wall

For numbers greater than a million, Ido uses the “long scale” of reckoning:

miliard billion (109)
bilion trillion (1012)
trilion quintillion (1018)
quadrilion septillion (1024)

Numbers can be made into nouns denoting groups or sets by adding -o. In these cases, numbers greater than ten are written as one word:

jazala trio a jazz trio
du dek-e-dui de ovi two dozen eggs

Ordinal Numbers

Ordinal numbers are those that express a thing’s position in a series, such as first, second, third. In Ido, ordinals are formed by adding -esm- to the equivalent cardinal number:

Unesme vi mustas trovar ... plusa arbustaro! Firstly you must find ... another shrubbery!
La triesma premio esas desengajeso. Third prize is you’re fired.
Nu, cadio esis dio speciala por me. Ol esis la cent-sep-nonesma dio sucedanta en qua me facis precize la sama kozo! Well, today was a special one for me. It was the hundred and seventy-ninth day in a row where I did exactly the same thing!

The suffix -esma is written -ma when written after a numeral, but -a when attached to a Roman regnal number, though it is still pronounced -esma in both cases:

Henrikus Va (read Henrikus kinesma) Henry V (read Henry the Fifth)

When asking for something requiring an ordinal number, one uses quantesma, which means “which one of the series?”:

« Qua dio esas? — Esas Kristonasko, Sioro! » “What day is it?” “It’s Christmas Day, sir!”
« Quantesma dio esas? — Esas la 25ma, Sioro! » “What day is it?” “It’s the 25th, sir!”

Fractional Numbers

Fractional numbers are those that express a value that is not a whole number, eg. half, a fourth, etc. In English, as in many European languages, these are mostly indistinguishable from ordinal numbers (eg., the fifth Beatle vs. a fifth of the Beatles), but in Ido are marked by the suffix -im- or, in more complex fractions, sur between two cardinal numbers:

dekeduimo a twelfth part
dek ed un duimo ten and a half
dek duimi ten halves
quaradek e tri sur cent forty-three hundredths
quaradek sur triacent forty three-hundredths
Triimo de la tero esis vorita da pudeli. A third of the earth was devoured by poodles.
Me ne konocas duimo de vi duime quante me volus, e me amas min kam duimo de vi duime quante vi meritas. I don’t know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

Multiplicative Numbers

Multiplicative numbers are those like English double, triple, and quadruple. In Ido, they are formed from the cardinal numbers by adding -opl-:

Duopligez vua plezuro, duopligez vua amuzo! Double your pleasure, double your fun!
Viv-asekuro saldas triople kande on mortas dum afer-voyajo. Life insurance pays off triple if you die on a business trip.
Quarople kin esas duadek. Four times five is 20.

Distributive Numbers

Distributive numbers are formed from cardinal numbers by adding -op-, which means “x at a time”:

La asaltanti venis duope. The stormtroopers came two at a time.
La sablani marchas unope por celar sua nombro. The sandpeople march single file to hide their numbers.
Quantope vu vendas la bileti? How many tickets at a time can you sell?


Some common operations in arithmetic:

Dek-e-kin plus tri esas dek-e-ok. Fifteen plus three equals eighteen.
Dek-e-kin minus tri esas dek-e-du. Fifteen minus three equals twelve.
Dek-e-kin per tri esas quaradek-e-kin. Fifteen times three equals forty-five.
Dek-e-kin sur tri esas kin. Fifteen divided by three equals five.
Dek potenco dua esas cent. Ten to the power of two is a hundred.
La tria radiko di duadek-e-sep esas tri. The cube root of twenty-seven is three.


There are two words for hour in Ido: horo, which indicates duration, and kloko, which indicates the hour of the day. Unlike in other languages, time in Ido is expressed only in terms of the current hour, never the coming hour, as in a quarter to three:

Qua kloko esas? What hour is it?
Cua tempo esas? What time is it?
Esas un kloko. It’s one o’clock.
Esas dek-e-un kloki e duimo. It’s eleven-thirty.
Esas kin kloki kinadek-e-kin. It’s five minutes to six.