CalculatorEnter your measurements below and it works the answer out.
Area divided by coverage, plus 10% waste, rounded up to whole squares. Enter what you measured and pick how it is sold.
The arithmetic. Work out the area, divide by what one square covers, add 10% waste, round up. Nothing more than that — the value of the page is the coverage figures and the waste allowance, both of which are stated here rather than hidden inside the tool.
Why the waste allowance is 10%. A square is 100 square feet — the unit the whole exterior trade quotes in, for siding and roofing alike. Ten per cent covers cuts at corners and openings; a house with a lot of gables and dormers wants fifteen.
How it is sold. Siding is sold by the square, and vinyl usually comes two squares to a box. Trim, corner posts and J-channel are counted in linear feet separately and are not in this figure.
Measure the openings honestly. Deduct large openings — a garage door, a picture window, a stairwell — and ignore small ones. Cutting a sheet or a board around a normal door wastes more material than the opening saves, which is why trades quote gross area and let the waste allowance absorb it.
Round up to how it is sold. A calculator that tells you 6.3 sheets is not finished. Everything below is rounded up to whole units, because that is what you can actually buy.
Divide your area in square feet by the coverage of one square, then add 10% and round up. At 100 sq ft each, a 200 sq ft job needs 3.
10% is what this calculator adds. A square is 100 square feet — the unit the whole exterior trade quotes in, for siding and roofing alike. Ten per cent covers cuts at corners and openings; a house with a lot of gables and dormers wants fifteen.
100 square feet. It is the unit the exterior trades quote in, so a 1,500 square foot wall area is 15 squares before waste.