Now that you’ve had a gist of the most useful numbers, let’s move to the writing rules for the tens, the compound numbers, and why not the hundreds, the thousands and beyond (if possible).
Numbers from zero to ten are specific words, namely zero [0], uno [1], due [2], tre [3], quattro [4], cinque [5], sei[6], sette [7], otto [8], nove [9], and dieci [10].
From eleven to sixteen, numbers are formed from the root of the digit followed by ten: undici [11], dodici [12], tredici [13], quattordici [14], quindici [15], and sedici [16]. From seventeen to nineteen, the order is reversed, as the unit is put directly after the ten: diciassette [17], diciotto [18], and diciannove [19].
The tens have specific names based on the matching digit root except for ten and twenty: dieci [10], venti [20], trenta [30], quaranta [40], cinquanta [50], sessanta [60], settanta [70], ottanta [80], and novanta [90].
Compound numbers are formed by juxtaposing the ten and the unit, causing an apocope of the last vowel of the ten name before a digit starting with a vowel, i.e. one and eight (e.g.: ventuno [21], trentadue [32], quarantotto[48]). When a compound number ends with three, tre becomes tré and the stress is put on the last syllable (e.g.: cinquantatré [53]).
The hundreds are formed by prefixing the word hundred by the multiplier digit, except for one hundred: cento[100], duecento [200], trecento [300], quattrocento [400]…
Hundreds, tens and units are linked together with no space (e.g.: centonove [109], duecentotrenta [230], novecentonovantanove [999]).
Thousands are formed by prefixing the word thousand by the multiplier digit, except for one thousand: mille[1,000] (plural mila), duemila [2,000], tremila [3,000], quattromila [4,000], cinquemila [5,000]…
Numbers are grouped in words of three digits, with the specific rule that a space is added after the word for thousand if its multiplier is greater than one hundred and does not end with a double zero (e.g.: duemilatrecentoquarantacinque [2,345], seicentomiladue [600,002], settecentosessantacinquemila duecento[765,200]).
The Italian language uses the long scale for big numbers where the naming pattern of the scale words alternates between the suffixes -ione and -iardo: milione (106, million), miliardo (109, billion), bilione (1012, trillion), biliardo(1015, quadrillion), trilione (1018, quintillion), triliardo (1021, sextillion)…
The digit one (uno) becomes un before a masculine noun, which is the case of all scale names. Besides, their plural construction is regular, the ending -e or -o becoming -i (e.g.: un milione [one million], due milioni [two million], un miliardo [one billion], due miliardi [two billion]).
