Standard canvas which is in most of the kits is 3.75, I think that is 4 stitches per inch. 5 count canvas will have more stitches per inch for a finer detailed latch hook rug and sometimes you will need to use a finer hook because it will have more stitches per inch than the standard 3.75. 18 count rug is stacks more finer again and I think you need to use a different needle all together. I assume with 18 count may not be used for a latch hook rug but some other craft, maybe locker hooking.It would have stacks more stitches per inch. I hope I have got that right :)