How much siding do I need for my house?

Calculate the total exterior wall area (width × height for each wall), add gable areas, subtract door and window openings, then add 10–15% for waste. Divide the adjusted area by your siding material’s coverage rate: vinyl covers ~200 sq ft per carton, fiber cement covers ~3.33 sq ft per plank, and 4×8 panels cover 32 sq ft per sheet. For a typical 1,500 sq ft home with standard openings, expect to need about 1,200–1,400 sq ft of siding material after deductions and waste.

What is a square of siding?

A "square" of siding is 100 square feet of coverage area. It’s the standard unit used by contractors and suppliers to estimate siding quantities. One carton of vinyl siding typically covers 2 squares (200 sq ft). When comparing prices or getting quotes, make sure everyone is using the same unit — price per square, price per carton, or price per linear foot can create confusion if mixed.

How do I calculate gable area for siding?

Gable area is a triangle: Area = 1/2 × Base Width × Gable Height. To find the gable height from roof pitch: Gable Height = (Base Width ÷ 2) × (Pitch ÷ 12). For example, a 30-foot-wide wall with a 6/12 pitch has a gable height of 15 × 0.5 = 7.5 feet, giving a gable area of 0.5 × 30 × 7.5 = 112.5 sq ft. Always include gable areas — they can add 15–25% to your total siding needs.

How much waste should I add for siding?

Add 10% for simple rectangular walls with few openings, 12% for moderate complexity, and 15% for walls with many gables, dormers, bay windows, or irregular shapes. The waste factor accounts for cutting around openings, fitting at corners, starter and finish courses, and damaged or defective pieces. Fiber cement and wood siding tend to generate more waste than vinyl due to breakage during cutting.

What is J-channel and how much do I need?

J-channel is a trim piece that creates a receiving channel where siding terminates at windows, doors, soffits, and other transitions. Calculate the linear footage as the perimeter of each opening (2 × width + 2 × height) times the number of identical openings. A standard 3×4 ft window needs about 14 linear feet of J-channel. Add 10% extra for cuts and overlaps at corners.

How many corner posts do I need?

You need one outside corner post at each exterior corner of the house and one inside corner post at each interior corner (L-shaped walls, bump-outs, etc.). Standard corner posts are 10 feet long. For walls taller than 10 feet, you’ll need to splice posts or use longer specialty posts. Count your corners from a top-down view of the house and add 1–2 extras for dormers and additions.

Which siding material is best for my project?

Vinyl is the most affordable and lowest-maintenance option, ideal for budget-conscious projects. Fiber cement (James Hardie) offers superior durability, fire resistance, and a natural wood appearance but costs 2–3× more installed. Wood lap provides authentic charm but requires regular painting or staining. Panel siding installs fastest on large wall areas and works well for garages, sheds, and modern designs. Consider your climate, maintenance tolerance, and budget when choosing.

Siding Calculator — Panels & Sheet Materials

How to Use the Siding Calculator

How to Calculate Siding Materials

Start by calculating the total wall area for every exterior wall: multiply each wall’s width by its height to get the rectangular area in square feet. If any walls have a gable (the triangular section under the roofline), add Gable Area = ½ × Width × Gable Height, where gable height is derived from your roof pitch: Gable Height = (Width ÷ 2) × (Pitch ÷ 12). A wall that is 40 feet long with a 9-foot height and a 6/12 gable has 360 sq ft of rectangular wall plus 33.3 sq ft of gable — a total of 393.3 sq ft for that wall alone.

Deducting Openings

Subtract the area of all doors and windows from the gross wall area. A standard 3′×6′-8" entry door takes away about 20 sq ft, while a typical 3′×4′ window removes 12 sq ft. Be precise — over-deducting means you’ll run short on material; under-deducting wastes money. After deducting openings, apply a waste factor of 10–15% to account for cutting, fitting, and damaged pieces. The industry standard is 10% for simple rectangular walls and 15% for walls with many cuts like gables and dormers.

Material Coverage Rates

Vinyl siding: Sold in cartons covering approximately 200 sq ft each (two “squares”). This is the most common residential siding material due to its low maintenance and competitive price.
Fiber cement (HardiePlank): Sold as individual planks, each covering about 3.33 sq ft (12′ × 8¼" exposure). Premium durability and fire resistance make it the fastest-growing siding choice.
Wood lap siding: Individual boards covering approximately 3 sq ft each depending on width and exposure. Requires painting or staining every 3–7 years.
Panel siding (T1-11, LP SmartSide): 4′×8′ sheets covering 32 sq ft each. Fastest installation for large wall areas with minimal cuts.

Accessories

Beyond the siding itself, you’ll need several accessories. Starter strip runs along the bottom of each wall to lock the first course — measure the total linear footage of all wall bases. J-channel wraps around every door and window to create a clean termination edge; calculate it as the perimeter of each opening times the quantity. Corner posts (inside and outside) cover vertical wall intersections — estimate one post per 10 feet of wall height at each corner. Finally, plan for trim around fascia, soffits, and gable ends based on your specific house design.

Pro Tips

Measure twice, order once. Take measurements from the outside of the house if possible. Interior measurements don’t account for sheathing thickness and can lead to underestimates.
Order from the same lot. Siding colors can vary between production runs. Order all materials from the same lot number to ensure consistent color across your entire project.
Account for overlap. Lap siding has an “exposure” that is less than the full board width. Coverage rates in this calculator already account for standard overlap, but verify with your specific product’s installation guide.

Free Siding Calculator — Panels & Sheet Materials