Siding Calculator
Siding is sold by the square — 100 square feet — so the job is gross wall area, minus doors and windows, plus waste, divided by 100. Runs 100% in your browser.
Siding Calculator
About this siding calculator
Siding quantity is a subtraction problem before it is a division problem: gross wall area, minus openings, plus waste, divided by 100 (one square = 100 sq ft, the unit suppliers quote for vinyl, fiber cement, and most other siding). Openings use planning sizes — about 21 sq ft per exterior door (3 × 7 ft) and about 15 sq ft per standard window — which is close enough because the waste allowance absorbs the difference. Our siding guide covers measuring, gables, and the trim budget.
Gables are the classic miss: a triangular gable end adds real area (base × height ÷ 2 per triangle), and on a two-story house the gables alone can add several squares. Measure each gable triangle, add the area in the gable field, and let the calculator carry it through. Houses with many gables, dormers, and openings should use the 15% waste figure — long straight runs can hold 10%, but complicated rooflines push waste up, never down.
The square count is the same for every siding type — vinyl, fiber cement, wood, and metal are all estimated by the wall area they cover — but how you buy differs: vinyl and aluminum are sold by the square in cartons, while fiber cement and wood lap siding are sold by the plank, so divide the order area by your product's coverage per piece. Trim is separate in all cases: corner posts, J-channel around windows, and starter strips run roughly 10–15% on top of the siding cost.
How to use
- Add up the length of every exterior wall and enter the total in feet, plus the wall height.
- Add any gable triangle area (base × height ÷ 2 per gable) or leave it at 0.
- Enter the number of exterior doors and windows (about 21 and 15 sq ft each are deducted).
- Pick a waste allowance — 10% simple, 15% for gables and complex houses — and optionally a price per square.
- Press Calculate for net area, squares, and the order quantity.
Good to know
- Assumes a single consistent wall height; split-level and multi-height houses should be measured in sections and added.
- Opening sizes are planning figures (21 sq ft per door, 15 per window) — oversized doors, sliders, and picture windows should be measured exactly and the difference adjusted by hand.
- Trim, flashing, housewrap, and labor are not included — budget trim at roughly 10–15% of siding cost.
Frequently asked questions
How much siding do I need for a 1,500 sq ft house?
A 1,500 sq ft single-story ranch has roughly 1,826 sq ft of wall — about 18.3 squares net, so order 21 squares with a 10% waste allowance.
What is a square of siding?
One square = 100 square feet of wall coverage — the standard unit vinyl, fiber cement, and most other siding types are sold in.
How much siding do I subtract for windows and doors?
About 21 sq ft per exterior door (3 × 7 ft) and about 12–15 sq ft per standard window. If you plan to trim around openings, subtract a little less.
Do gables need extra siding?
Yes — gable triangles add area. Measure each triangle (base × height ÷ 2) and add it in the gable field; houses with many gables should use 15% waste.
How many squares of siding for a 2,000 sq ft house?
A 2,000 sq ft two-story house typically needs 24–28 squares — its exterior walls total roughly 2,400–2,800 sq ft depending on footprint, before waste.