Siding Estimator
Enter your wall dimensions to estimate siding — sold by the "square" (100 sq ft), with waste for cuts.
Runs entirely in your browser — your numbers never leave this page.
How it works
Siding is sold by the square — 100 sq ft of coverage. The math is wall area minus openings, plus waste:
Squares = (Wall length × Height − Openings) × (1 + Waste) ÷ 100
- Measure every wall being sided and add them up; gable triangles are (base × height) ÷ 2.
- Deduct openings: ~15 sq ft per window, ~21 sq ft per door — or measure the big ones.
- Waste: 10% for straight ranch walls, 15–20% with gables, corners, and bump-outs — every cut wastes a piece.
- Housewrap first: siding is the rain screen, not the waterproofing — Tyvek/Typar underneath does the real work.
- Buy extra: 1–2 spare squares for repairs. Manufacturers discontinue colors; a future patch from a new dye lot will show.
Frequently asked questions
How much siding do I need?
Wall area minus windows/doors, divided by 100, plus waste. 120 ft of 9-ft walls (1,080 sq ft) minus 200 sq ft of openings = 880 → +10% = 968 sq ft ≈ 9.7 squares.
What is a "square" of siding?
100 square feet of coverage. It is the standard unit for siding, roofing, and most cladding — always round up.
How do I measure gables?
Each gable triangle is (base × height) ÷ 2. Add both gables to the rectangle walls before deducting openings.
Should I deduct windows and doors?
Yes for large openings — it saves real money on big jobs. Small windows under ~10 sq ft are often left in as built-in waste allowance.
How much waste should I add?
10% for simple walls, 15% with gables and corners, 20% for complex shapes. Vinyl cuts waste more than fiber cement (which comes in longer boards).
Do I need housewrap under siding?
Yes — siding sheds most rain but is not waterproof. Housewrap (Tyvek/Typar) over sheathing is the actual water barrier; skip it and sheathing rots.
Vinyl vs fiber cement — how much more?
Fiber cement (Hardie) needs ~15% fewer cuts wasted but costs 2–3× installed. Material-only, vinyl runs ~$1–2/sq ft, fiber cement ~$2–4/sq ft.
How do I estimate soffit and fascia?
Soffit: eave length × overhang width. Fascia: total eave + rake length in linear feet. Both are ordered separately from wall siding.
Can I side over old siding?
Vinyl over old wood sometimes; never over rotten sheathing. Strip to inspect — hidden rot is the expensive surprise.
Why buy extra squares?
For repairs. Siding colors get discontinued and dye lots shift — a patch from a different lot is visible from the street. 1–2 spare squares in the garage solves it.