What is a siding "square"?

In the siding industry, a "square" is equal to 100 square feet of wall area. Most vinyl siding is sold and priced by the square.

How much waste should I add for gables?

Gables produce more waste due to the angled cuts. Add 15–20% waste for gable-heavy designs, whereas 10% is usually enough for simple rectangular walls.

Should I remove old siding before installing vinyl?

Removing old siding allows you to inspect for rot and ensure a flat surface. However, vinyl can be installed over some existing surfaces using fan-fold insulation or strapping if the surface is stable and flat.

Exterior Estimating

Vinyl Siding Calculator

Accurately estimate the amount of vinyl siding needed for your project. Enter wall dimensions, account for windows and doors, and calculate square footage for gables to find the total "squares" required.

Vinyl Siding Calculator

Estimate siding order area, squares, and panel count (minus openings) with waste allowance

Calculation method

Waste allowance

Building perimeter

Wall height

Gable / dormer area (optional)

Openings (doors/windows)

Per-box coverage (optional)

Panel length

Panel exposure (visible height)

Tip

Use package specs

Panel length and exposure depend on the profile (D4/D5, etc.). Use the manufacturer spec sheet for best results.

Results

Enter dimensions above to calculate

Calculating Wall & Gable Areas

Siding area equals the wall rectangles plus gable triangles, minus the openings for windows and doors.

Necessary Siding Accessories

Don't forget to estimate the trim and accessories. Siding cannot be installed without these critical components.

Accessory	Measurement	Purpose
Starter Strip	Linear Feet/Metres	Secures the first course of siding
J-Channel	Linear Feet/Metres	Trims windows, doors, and gables
Outside Corners	Vertical Feet/Metres	Protects and trims external wall corners
Inside Corners	Vertical Feet/Metres	Trims internal wall corners
Undersill Trim	Linear Feet/Metres	Finish trim for top courses and windows

Step-by-Step Formulas

1. Gross Wall Area

Area = Wall Length × Wall Height

Measure the total area of all exterior walls to be sided. For gables, calculate the triangular area (Base × Height ÷ 2). Sum all areas for a gross total.

2. Subtract Openings

Net Area = Gross Area − (Windows + Doors)

Subtract the area of all windows, doors, and other penetrations. Vinyl siding is sold in "squares" (100 sq ft), so accurate net area prevents over-ordering.

3. Waste Allowance

Order Area = Net Area × (1 + Waste%)

Add 10% for simple jobs. For complex projects with many gables, corners, or small sections, add 15–20% to account for offcut loss.

4. Convert to Squares

Squares = Order Area ÷ 100

Dividing the total square footage by 100 gives you the number of "squares" to order. Siding, soffit, and underlayment are typically priced and packaged by the square.

Worked Example

One-story house: Four walls (30' × 10'), two gables (30' base × 10' high), 80 sq ft of openings, 10% waste.

Walls Area = 4 × (30 × 10) = 1,200 sq ft

Gable Area = 2 × (0.5 × 30 × 10) = 300 sq ft

Gross Area = 1,200 + 300 = 1,500 sq ft

Net Area = 1,500 − 80 = 1,420 sq ft

Order Area (+10%) = 1,420 × 1.10 = 1,562 sq ft

Squares = 1,562 ÷ 100 ≈ 15.6 Squares

💡 Pro tip

Vinyl siding expands and contracts with the temperature. When nailing siding, never drive the nails tight—leave a small gap (about the thickness of a dime) between the nail head and the siding hem. This allows the panels to slide freely as they heat and cool, preventing buckling.

Frequently Asked Questions

What is a siding "square"?: A "square" is 100 square feet of wall area. Most siding and underlayment materials are sold and priced by the square.
How much waste should I add for gables?: Angled gable cuts create more offcut waste. Add 15–20% for gables, compared to 10% for standard walls.
Can I install vinyl over old siding?: Yes, if the surface is flat and stable. Use fan-fold insulation as a level underlayment, though removing old siding is better for inspecting the structure.