This siding calculator turns wall dimensions into an order: gross wall area minus windows, doors and gable adjustments, plus a waste allowance — reported in square feet, siding “squares” and panels for common profiles.
Gross area shortcuts: rectangular walls are length × height; a gable end is a triangle (½ × base × peak height above the wall plate) — add it to that wall. Trim (J-channel, corners, starter strip) is ordered by linear feet of edges and openings, separately from field area.
Squares, Panels and the Shape of a Wall
Siding trades in squares (100 sq ft of coverage) regardless of material — vinyl, fiber cement, wood or metal — while installation counts individual pieces by their exposure: a 12.5 ft vinyl panel showing 8 inches of face covers about 8.3 sq ft (the default here); double-4, Dutch lap and board-and-batten each carry their own exposure math on the carton. Openings come off the gross (nobody sides over a window), and corners/gables decide the waste factor: simple rectangles run 5–10%, gable-heavy or diagonal installs 12–15%+. Finishing surfaces instead? Our Paint Calculator covers the coating route. Part of our Construction Calculators collection.
Worked Example (Verified)
A house with 1,440 sq ft of wall (including two gable triangles) and 200 sq ft of windows/doors:
- Net field area: 1,440 − 200 = 1,240 sq ft
- With 10% waste: 1,364 sq ft → 13.6 squares (order 14 squares of material)
- Panels at 8.3 sq ft coverage: ⌈1,364 ÷ 8.3⌉ = 165 panels
- Reality check the order: a 24 × 40 ft single-story with 9 ft walls has 1,152 sq ft of rectangle before gables — if your gross number lands far from your house’s perimeter × height (+ gables), remeasure before ordering, not after delivery
What the Field Area Doesn’t Include
- Trim package: outside/inside corners, J-channel around every opening, starter strip along the bottom, utility trim at the top — measured in linear feet off the plan, and chronically under-ordered by first-timers.
- Housewrap/weather barrier by the roll (typically 10–15% lap waste), flashing tape, and fasteners.
- Soffit and fascia are their own areas and materials — don’t let the field number swallow them.
- For fiber cement, add blades and dust control to the plan; for vinyl, add a zip tool and patience for expansion gaps.
Related Tools
- Paint Calculator — coating walls instead of covering them
- Roofing Calculator — the other great exterior surface
- Construction Calculators — the full collection
Frequently Asked Questions
How do I calculate how much siding I need?
Total wall area (length × height per wall, plus ½ × base × height for each gable triangle), minus window and door areas, plus 10% waste. The example: 1,440 − 200 = 1,240 sq ft → 1,364 sq ft ordered = 13.6 squares.
What is a “square” of siding?
100 square feet of installed coverage — the trade’s universal unit across materials. Cartons are labeled by the squares (or fraction) they cover at the stated exposure.
How much waste should I allow?
10% for straightforward rectangular walls; 12–15% with many gables, bump-outs or diagonal/herringbone patterns; 5–7% for a pro crew on a simple ranch. When in doubt, the higher number — matching a dye lot later is harder than returning a carton.
Do I subtract windows and doors?
Yes — siding doesn’t cover them, and their area is real money (200 sq ft = 2 squares in the example). Measure each opening’s rough dimensions; don’t subtract anything smaller than ~3 sq ft if you prefer the waste built in instead.
How many panels are in a square?
It depends on exposure: at 8.3 sq ft per panel a square needs ~12 panels; narrower exposures (single-6 board) need more pieces per square. Divide 100 by your panel’s coverage from its carton — this calculator’s panel field does exactly that against your order area.
Is this siding calculator free?
Yes — free, instant, no sign-up.