Most of this is just taken from stuff I’ve typed up as drafts for a textbook, but I’ve added things in and if you don’t understand anything just ask. I figure most of you readers know this stuff already but there were a few people who were interested in learning Icelandic and who weren’t already, on the Facebook. If I made any mistakes, let me know.

Numbers one through four decline based on the gender and number of the noun they are describing, after that most don’t. If you don’t know what I mean by this, just ask and I can do a post on it later.

Nominative/Dictionary case:

Einn / Ein / Eitt / Einir – one
Tveir / Tvær / Tvö / Tvennir – two. Et cetera.

Singular numbers are used just like numbers in English. Plural numbers are used when you have pairs of something (tvennir skór – two pairs of shoes). If you say “tveir skór”, it means you have two shoes but they’re not a pair.

Use masculine numbers when talking about: kennitalas (SSNs), phone numbers, centimeters, deciliters, the words “klukkutímar” and “tími”
Feminine when: minutes, teaspoons
Neuter when: kilos, the word “klukkan”, house numbers

5 Fimm
6 Sex
7 Sjö
8 Átta
9 Níu
10 Tíu
11 Ellefu
12 Tólf
13 Þréttán
14 Fjórtán
15 Fimmtán
16 Sextán
17 Sautján
18 Átján
19 Nítján
20 Tuttugu
21 Tuttugu og einn
30 Þrjátíu
40 Fjörutíu
50 Fimmtíu
60 Sextíu
70 Sjötíu
80 Áttatíu
90 Níutíu
100 Hundrað
101 Hundrað og einn
200 Tvö hundruð
1.000 Þúsund
1.000.000 Milljón

“Hundrað og einn”. You always add og (and) right before the last number said. 532, fimm hundruð þrjátíu og tvö. 530, fimm hundruð og þrjátíu.

“Eitt hundrað” – einn isn’t just a letter, it actually means one, alone, and “the one”. But because “einn” is singular, then “hundrað” is also singular. If saying tvö hundruð, “tvö” is plural (as in more than one, not that the word is in its plural form) so “hundruð” is also plural.

1950 (date)  – Nítjan hundruð og fimmtíu.
1950 (money) – Eitt þúsund og fimmtíu, or also nítjan hundruð og fimmtíu. You can only say the ” — hundred” form if the money is less than two thousand – after that, you have to say the “— thousand, — hundred” form. Years are always in the “— hundred” form. You should never say it like “nítjan-fimmtíu” or something, like “nineteen-fifty” in English (I mean when you shorten things like thirty-five fifty-six instead of three thousand, five hundred and fifty-six for 3556). They don’t do that in Icelandic apparently.

This is just half of what I’m going to post about numbers, the next post will be the second half. Really, if there’s anything you don’t understand or if you have any questions even if you think they’re really stupid, please ask.