Siding Calculator: Squares, Panels & Square Footage

Add up the perimeter of all exterior walls, multiply by the wall height, and you have gross siding area. For a 30×40 ft single-story home with 9 ft walls, that’s a perimeter of 140 ft × 9 ft = 1,260 sq ft.

Subtract the area of every door, window, and opening. Then add gable end areas if your home has gables. Finally, multiply by 1.10 to account for trim, overlap, and offcuts.

Gable ends are easy to miss. Each gable is a triangle: (base × height) / 2. For a 30 ft wide house with a 6/12 pitch roof, each gable is about 113 sq ft.

Two gables (front and back) add ~225 sq ft to your siding total — that’s a meaningful chunk you don’t want to leave out.

House siding is calculated by exterior wall surface area, which is different from house square footage (which measures interior livable space). To estimate siding correctly, you need the actual wall surface area accounting for gables, eaves, and overhangs.

Base calculation: house perimeter × wall height + gable triangles. For a 40 × 30 ft single-story house with 8 ft walls: perimeter (140 ft) × 8 ft = 1,120 sq ft of wall. Add gable triangles for the ends: 30 ft wide × 6 ft peak ÷ 2 = 90 sq ft per gable × 2 gables = 180 sq ft. Total: 1,300 sq ft.

Two-story house doubles the wall area. A 40 × 30 ft two-story: 1,120 × 2 + 180 = 2,420 sq ft of siding area.

Subtract major openings (windows >10 sq ft, doors): a typical house has 200-400 sq ft of windows and doors. Net siding area: 2,000-2,200 sq ft for the example two-story house.

Material choice moves the total more than house size does. The installed ranges below are 2026 US planning estimates covering material, tear-off of the old cladding, house wrap and labour. They shift with region, storey count and how much trim detail the elevation carries.

Read the lifespan column next to the price before deciding. Vinyl is the cheapest way to clad a house. Fibre cement costs roughly double and lasts twice as long, which is why it wins on cost-per-year even though it loses on sticker price. Wood is the only material here that asks for money again every few years.

Siding is sold by the square, not the square foot. One square covers 100 sq ft of wall. Suppliers quote in squares, delivery tickets list squares, and vinyl usually ships two squares to a carton — so converting wall area into squares is the last step before you order.

The maths is short. Take your net wall area (gross wall minus doors and windows), add waste, divide by 100, then round up to a whole square. Nobody sells a third of a square.

Waste runs about 10% on a plain rectangular elevation and climbs toward 15% once gables, dormers or heavy window trim enter the picture, because every angled cut leaves an offcut too short for the next course. The table assumes 10%.

Worked example — 1,500 sq ft of net wall. Add 10%: 1,650 sq ft to order. Divide by 100: 16.5 squares. Round up and order 17. Keep the offcuts until the job passes inspection; a cracked panel is easier to replace from your own scrap than from a fresh dye lot.

Siding alone isn't a full exterior project. A complete re-siding includes:

Tear-off of existing siding: $1-3 per sq ft.

House wrap / weather barrier: $0.20-0.50 per sq ft.

Trim around windows, doors, corners: $5-15 per linear foot.

Soffit and fascia (under the eaves): $8-20 per linear foot of eave.

Gutters (often replaced during siding work): $5-15 per linear foot.

Sealing and caulking: included in install labor.

For a 2,000 sq ft siding project, expect total cost of $10,000-30,000 fully installed depending on material. Vinyl is the cheap end ($8,000-14,000), fiber cement is the popular middle ($15,000-25,000), and natural wood or stone is the high end ($20,000-50,000+).