my room measures 216 inches by 252 iches. box covers 17.59 sq feet. how many boxes do i need

378 sq feet of room using carton that each cover 17.59 sq ft would require exactly 21.5 cartons. Unfortunately, there is always waste from cutting and normal manufacturer recommendations are to add 10% to your required minimum would would be 24 cartons. If you are careful on your cuts and also try to use your remnants, you could only need less than 5% extra. Good luck.

You'll need a minimum of 22 boxes, but I'd suggest getting 1-2 extra.