1 through 20

The cardinals 1 through 4 decline. 5 through 20 do not.

The four declinable numerals einn, tveir, þrír and fjórir will decline whenever it appears in a number.

Multiples of ten

Multiples of ten from 30 to 110 are expressed by combining a cardinal number with the plural of the u-stem masculine noun tigr "ten," whose declension is given below.

Nouns counted with multiples of ten are in the genitive case, as in the sentence þrír tigir manna dóu "thirty men died," literally meaning "three tens of men died."

For multiples of ten other than 30 and 40, while tigr declines, the preceding cardinal number does not. For 30 and 40, þrír and fjórir decline as well as tigr. For example, see how, in the following sentences, þrír "three" in the first sentence declines to the masculine accusative plural while fimm "five" in the second does not.

• Hann slógu þrjá tigu manna. He slew thirty men.
• Hann slógu fimm tigu manna. He slew fifty men.

Other numbers 21 through 119

Other numbers are like English but with an ok ("and") connecting the multiple of ten and the single digit. Examples are þrír tigir ok tveir or tveir ok þrír tigir "thirty-two," ellifu tigir ok sjau or sjau ok ellifu tigir one hundred seventeen; eleven tens and seven."

hundrað and þúsund

The neuter noun hundrað "long hundred; 120" declines like the following.

The feminine noun þúsund "long thousand; 1200" declines like the following.

Nouns counted with hundrað and þúsund are in the genitive form.

Einn, tveir, þrír and fjórir

Einn, tveir, þrír and fjórir appearing in numbers ending in 1, 2, 3 or 4 will decline.

If the subject is modified by a number that ends in 1, the verb is in the singular form. Otherwise, the verb is in the plural form. See the following examples.

• Einn maðr ok þrír tigir dó. Thirty-one men died.
• Fimm tigir manna ok tveir dóu. Fifty-two men died.