Siding Calculator

The formula

Coverage and yield assumptions

A square of siding covers 100 sq ft of wall; vinyl cartons usually hold two squares. The Vinyl Siding Institute's installation manual covers trim such as J-channel, starter strip and corner posts, which are counted by length rather than area. Fiber cement planks are sold by the piece; divide the net area by the exposed face (for example 7 in exposure × 12 ft = 7 sq ft).

Measuring the walls

Measure the perimeter of the house at the foundation and the height from the bottom of the siding to the eaves. Measure each gable's width at the eave line and the height from eave to peak. For dormers and bump-outs, add them as small rectangles and triangles. Subtract windows and doors larger than about 20 sq ft each; smaller openings can be left in as waste.

Trim and accessories

• Outside corner posts: one per outside corner, the height of the wall.
• J-channel around every window and door and along soffits.
• Starter strip along the bottom of every wall.
• House wrap behind the siding, sold in rolls of 9 ft or 10 ft width.

Choosing siding

Vinyl is light, affordable and low maintenance but can crack in cold impacts. Fiber cement is heavy and durable, holds paint well and resists fire. Engineered wood is lighter than fiber cement and easy to cut. Natural wood needs regular finishing. Each has its own installation rules for clearances above grade and roofs.

Installation tips

Vinyl must hang loose on its nails to expand and contract, so nails go in the center of slots with about 1/32 in left under the head. Overlap ends about 1 in and stagger joints between courses. Keep siding at least 6 in above grade unless the manufacturer allows less.

Common mistakes to avoid

• Ignoring the gable triangles.
• Nailing vinyl tight so it cannot expand.
• Forgetting corner posts, J-channel and starter strip.
• Skipping house wrap or flashing at windows.
• Leaving too little clearance above grade or roofs.

Waste factor

10% is common for simple houses. Use 15% for houses with many windows, dormers, gables and corners; complicated cuts around openings add up.

Imperial and metric

Switch the toggle above the inputs to enter ft ↔ m, sq ft ↔ m². The page converts metric entries to imperial before calculating, using NIST factors (1 ft = 0.3048 m, 1 in = 2.54 cm), and shows key results in both systems.

Worked examples

Single-story house

Inputs: house perimeter 140 ft; wall height (to eaves) 9 ft; gable ends 2; gable width 30 ft; gable height (peak above eave) 7 ft; doors + windows area 150 sq ft; waste factor 10%.

Result: You need 14.5 squares of siding (1,452 sq ft).

• Units to buy (rounded up): 15 squares
• Gross wall + gable area: 1,470 sq ft (136.6 m²)
• Net after openings: 1,320 sq ft (122.6 m²)

Two-story with four gables

Inputs: house perimeter 160 ft; wall height (to eaves) 18 ft; gable ends 4; gable width 24 ft; gable height (peak above eave) 8 ft; doors + windows area 320 sq ft; waste factor 15%; cost per unit $240.

Result: You need 33.9 squares of siding (3,386 sq ft).

• Units to buy (rounded up): 34 squares
• Gross wall + gable area: 3,264 sq ft (303.2 m²)
• Net after openings: 2,944 sq ft (273.5 m²)
• Estimated material cost: $8,160.00

Garage walls only

Inputs: house perimeter 96 ft; wall height (to eaves) 8 ft; gable ends 0; gable width 0 ft; gable height (peak above eave) 0 ft; doors + windows area 80 sq ft; waste factor 10%.

Result: You need 7.6 squares of siding (757 sq ft).

• Units to buy (rounded up): 8 squares
• Gross wall + gable area: 768 sq ft (71.3 m²)
• Net after openings: 688 sq ft (63.9 m²)

Quick reference for common sizes

The table repeats the first worked example at smaller and larger sizes, keeping every other setting the same, so you can see how the siding calculator result scales.

Limitations

The estimate covers walls and simple gables. Soffit, fascia and trim pieces are sold by length. Multi-story houses with varying heights should be measured wall by wall.