Siding Squares Calculator
Add up your wall and gable area, take out the doors and windows, then add a waste allowance to see how many squares of siding to order. One siding square covers 100 sq ft — the same unit your supplier quotes.
Calculator
140 ft perimeter × 9 ft, plus 150 sq ft of gables, minus 180 sq ft of openings is 1,230 sq ft — with 10% waste, order 13.5 squares.
Siding, like roofing, is sold and installed by the square — a 100 sq ft unit of finished wall. To turn a house into an order you need the net wall area: the gross rectangle of every wall, plus the triangular gable ends, minus the large openings you will not cover. Dividing that by 100 gives squares; a waste allowance covers cut-off, trim laps and the odd damaged piece.
Measure the walls as simple rectangles (perimeter × height), handle each gable as a triangle, and only subtract the openings that are genuinely large — garage doors, patio doors, picture windows. Leaving small windows in the count is a common, deliberate way to build in a little extra material.
Formula
The take-off is one net-area sum followed by a division:
net = perimeter × height + gable area − openings
squares = (net ÷ 100) × (1 + waste %)
- perimeter × height — the gross wall rectangle (sq ft).
- gable area — ½ × width × height for each gable end.
- openings — the large doors and windows you subtract.
- waste % — 10% simple, up to 15% on a cut-up elevation.
Worked example
Take a house with a 140 ft perimeter, 9 ft walls, two gables totaling 150 sq ft, and 180 sq ft of doors and windows, at 10% waste:
- Gross walls: 140 × 9 = 1,260 sq ft.
- Add gables: 1,260 + 150 = 1,410 sq ft.
- Subtract openings: 1,410 − 180 = 1,230 sq ft net.
- To squares: 1,230 ÷ 100 = 12.3 squares.
- Add 10% waste: 12.3 × 1.10 = 13.5 squares to order.
So a house that measures 12.3 squares of actual wall is ordered as about 13.5 squares.
Measuring & ordering tips
A siding square is 100 sq ft, identical to a roofing square, so the same ordering language carries over from the roof. The two numbers that trip people up are gables and openings.
Gables. A gable is a triangle: its area is ½ × base width × vertical height. On a 30 ft-wide gable that rises 5 ft to the ridge, that is ½ × 30 × 5 = 75 sq ft per end. Add every gable into the Total gable area field. If you know the roof pitch and the run, our roof tools give you the gable rise directly.
Openings. Subtract only the big ones. Many estimators leave small and medium windows in the wall area on purpose: the off-cuts around each opening become part of the real-world waste, so counting the opening as solid wall quietly covers it. If you subtract every opening, keep your waste percentage toward the higher end.
Waste. A plain rectangular box with few corners runs about 10%. A cut-up elevation — lots of corners, dormers, a steep pitch, staggered courses — runs 12–15%. Waste is never wasted money you can skip: it is the material that ends up on the wall as trimmed pieces.
Frequently asked questions
How many squares of siding is my house?
Add the gross wall area (perimeter × height) and the gable triangles, subtract the large openings, then divide by 100 — one square is 100 sq ft. Finally add a waste allowance. The worked example above turns 1,230 sq ft of net wall into about 13.5 squares to order at 10% waste.
Do I subtract windows and doors from siding?
Subtract only the large openings — garage doors, sliding-glass doors, picture windows. Small and medium windows are often left in the wall area on purpose, because the off-cuts around them become part of your waste. If you do subtract every opening, use a slightly higher waste percentage to compensate.
What is a siding square?
A square is 100 square feet of finished wall — the same unit used for roofing. Suppliers price and quote siding by the square, so converting your measured wall area into squares makes ordering and comparing quotes straightforward.
How much waste should I add for siding?
About 10% on a simple, rectangular house, and 12–15% on a cut-up elevation with many corners, dormers or a steep roof. Waste is the material that becomes trimmed pieces on the wall, so it is a real part of the order, not padding.
How do I measure a gable?
Treat each gable as a triangle: area is one-half of the width times the vertical height to the ridge. A 30 ft-wide gable rising 5 ft is ½ × 30 × 5 = 75 sq ft. Add every gable end into the total gable-area field.