Counting in Sindarin is a little different than you are used to. Like English, you break the number into thousands, hundreds, tens, and ones columns, but in Sindarin, this is done backwards. We know this because of how numbers are written. Unfortunately, we know more about writing Sindarin numbers in script than we know about how they would be pronounced. If you need to write a number that we don't know how to say, just write it with numerals, backwards. So, "4100" would be written, "0014."
Elves preferred to count time in sixes and twelves, but their counting system itself was base-10.
These are the numbers that one uses when counting. They communicate the amount of something.
Multiples of ten:
20 *taphaen
30 *nelphaen
40 *cambaen
50 *lephaen
60 *enephaen
70 *odophaen
80 *tolophaen
90 *nederphaen
For making the numbers in-between, a common approach is to use the word "and" a(r) between the numbers, listing the smaller numbers first, then the larger multiples of ten.
Don't forget to include the vocalic mutation that follows a.
21 min a *daphaen
32 tâd a *nelphaen
43 neledh a *gambaen
54 canad a *lephaen
65 leben ar *enephaen
76 eneg ar *odophaen
87 odog a *dolophaen
98 tolodh a *nederphaen
We also have host for 144 in the Etymologies, but we find that root still being used later on as a suffix for groups of hated or feared creatures. This probably isn't a number like the others so much as a fixed number for a certain quantity, like "a baker's dozen" or "a gross."
The other number we know is Sindarin is meneg for 1000, isolated from Menegroth "1000 Caves." But, this could also mean "a myriad." Elves though, with their long lifetimes, would probably be able to count this high, so this probably is an actual number.
When attached to a noun, Cardinal Numbers replace "the" in the word order. We don't know if they cause mutation or not, so I shall err on the side of not for now.
min lavan - one animal
taphaen levain - 20 animals
Ordinals are the number-adjectives used to put things into a specific numerical order.
1st main/minui/erui
2nd taid/tadui
3rd nail/nelui
4th cannui
5th *lemmui
6th engui
7th othui
8th tollui
9th nedrui
10th paenui
Last medui
For the rest of the numbers, since they are made from compounds, we can just add -ui onto them.
11th *minibui
12th *ýnegui
20th *taphaenui
30th *nelphaenui
For 1000th, we can reconstruct *mengui.
When you have a more complex number, only add -ui to the last part of the number.
25th leben a *daphaenui
92nd tâd a *nederphaenui
66th eneg ar enephaenui
In Sindarin, these are adjectives. They follow their nouns and the first element of the number is lenited.
Examples of Ordinal Numbers in use:
Aur gannui - Fourth morning
Aew veren dâd ar *enephaenui - Sixty second happy bird