Siding Calculator

Quick Answer

Last updated: 3 November 2026 ·How we calculate this: wall and gable area with a waste allowance

How This Siding Calculator Works

Measure around the outside of the house to get the perimeter, and measure the wall height from the foundation to the eaves. Add the gable ends, the triangles under the roof peaks, and the total area of doors and windows. The calculator finds the wall and gable area, takes off the openings, adds a waste allowance and gives the result in square feet and in squares.

How to Use the Siding Calculator

1. Measure the perimeter of the house.
2. Measure the wall height to the eaves.
3. Enter the number and size of gable ends.
4. Add up the area of doors and windows, and choose a waste allowance.
5. Press Calculate and read the square feet and squares to order.

Core Formulas

• Wall area: perimeter × wall height
• Gable area: number of gables × width × height ÷ 2
• Net area: walls + gables − doors and windows
• Order: net area × (1 + waste %)
• Squares: order ÷ 100, rounded up

Key Terms

• Square: 100 square feet of siding coverage.
• Gable: the triangle of wall under the peak of a pitched roof.
• Eaves: the lower edge of the roof that overhangs the wall.
• J-channel: trim that holds siding edges around windows and doors.
• Exposure: the part of a siding board that shows after it is installed.

Worked Example

Using the example house above:

• Walls = 160 × 9 = 1,440 sq ft, and gables = 2 × 30 × 8 ÷ 2 = 240 sq ft
• Net = 1,440 + 240 − 180 = 1,500 sq ft
• With 10% waste: 1,650 sq ft, so order 17 squares

Real-Life Examples

• Ranch house: 180 ft around, 8 ft walls and two 28 × 6 ft gables, minus 200 sq ft of openings, needs 16 squares with 10% waste.
• Garage: 24 × 24 ft with 9 ft walls and two gables 24 × 6 ft, minus a 16 × 7 ft door, needs 10 squares.
• Shed: 10 × 12 ft with 7 ft walls and no gables needs 4 squares.
• Budget: add your price per square to see the siding cost.

Vinyl vs Fiber Cement Siding

• Vinyl: lighter, usually cheaper and quicker to install.
• Fiber cement: heavier and often costs more, but resists fire and impact well.
• Either way: the square footage you need is about the same.

Squares by Wall Area

What Changes the Amount

• House shape: many corners and bump-outs mean more cutting and waste.
• Siding type: vinyl, fiber cement and wood have different coverage and waste.
• Exposure: the visible width of each board affects coverage per piece.
• Openings: many small windows add trim work but save little siding.

For a house with an attached garage or an L shape, measure each outside wall where siding will go and add the lengths, rather than using the floor plan size. Skip walls covered by brick or stone, and measure them separately if you plan to side them later.

Common Mistakes to Avoid

• Forgetting the gables. They can add hundreds of square feet.
• Using the roof peak height for all walls. Measure walls to the eaves, then add gables separately.
• No waste allowance. Cuts and corners always use extra.
• Subtracting every small window. Pieces around them are often wasted anyway.
• Forgetting trim and accessories. Corners, J-channel and starter strip are extra.

Frequently Asked Questions

References & Sources