Vinyl-siding-square-feet-per-box, estimating how much siding you’ll need to complete your project can be confusing when you’re trying to figure out where you’ll have waste and where you’ll need to order extra. vinyl siding comes in 12-foot-long strips that are about 1 foot wide, depending upon the style.. Square feet in a box of vinyl sideing? answer save. 6 answers. relevance. hebers1. 1 decade ago. favorite answer. despite the previous answers a box of siding will always have 2 square (that is 200 square feet) of siding in them no matter what brand it is. source(s): contractor / carpenter for 10 years. 0 0 0.