Siding Calculator

1. Enter the wall perimeter (the total length around all walls) and the wall height in feet.
2. Add the number of gables and each gable's width and height. Enter 0 gables if the walls are square at the top.
3. Enter how many doors and windows to subtract. The tool uses 21 sq ft per door and 12 sq ft per window.
4. Set a waste factor (10% is typical) and a price per square if you want a cost.
5. Read the net siding area, the squares to order and the estimated cost.

A siding calculator estimates how much exterior siding you need to cover the walls of a building. Siding is sold by the square, where one square covers 100 square feet of wall. Getting the square footage right is the first step to ordering the correct amount.

The job has three parts. First, the flat wall area, which is the perimeter times the height. Second, the triangular gable ends above the walls. Third, the openings for doors and windows, which you subtract because you do not side over them.

Adding a waste allowance covers cuts, trim pieces and corners. See the construction calculators hub for more building estimators.

The calculator adds wall and gable area, subtracts openings, then applies waste and converts to squares.

1. Multiply the wall perimeter by the wall height for the flat wall area.
2. Find each gable area with the triangle formula and multiply by the number of gables.
3. Subtract the area of doors and windows.
4. Add the waste factor, then divide by 100 to get squares and round up to whole squares.

Why Siding Uses Squares

A square is an industry unit equal to 100 square feet. Vinyl, fiber cement and other siding products are priced and packaged around this unit, so quoting a job in squares keeps orders and bids on the same footing.

Take a house with a 120 ft wall perimeter, 9 ft tall walls, two gables each 24 ft wide and 6 ft high, two doors, six windows, a 10% waste factor and a price of $300 per square.

Wall area: 120 x 9 = 1,080 sq ft.

Gable area: 2 x 0.5 x 24 x 6 = 144 sq ft.

Openings: 2 doors x 21 + 6 windows x 12 = 42 + 72 = 114 sq ft.

Net area: 1,080 + 144 - 114 = 1,110 sq ft.

With 10% waste: 1,110 x 1.10 = 1,221 sq ft.

Squares: 1,221 / 100 = 12.21 squares, rounded up to 13 whole squares.

Cost: 13 x $300 = $3,900. If you prefer to price the exact figure, 12.21 x $300 is about $3,663, but suppliers sell whole squares, so most buyers order 13.

The square footage is the same whatever product you pick, but coverage, price and waste differ.

Vinyl Siding

The most common and lowest-cost option. It is light, low-maintenance and sold in boxes that cover a set number of squares. Waste is usually low, around 10%, on simple walls.

Fiber Cement Siding

A durable, fire-resistant board (often sold under brand names) that mimics wood. It costs more than vinyl and is heavier to handle, but it lasts longer. Budget a slightly higher waste factor for cutting.

Wood and Engineered Wood

Natural wood clapboard or engineered wood panels give a classic look and need regular paint or stain. Waste can be higher because of grading and defect cuts.

Always check the coverage printed on the box or data sheet, since it can vary by profile and exposure.

Accurate measurements make the estimate reliable. Here is how to gather the numbers.

Wall Perimeter

Measure the width of each wall at ground level and add them together. For a simple rectangular house that is 2 x (length + width). Only count walls that will actually be sided.

Wall Height

Measure from the bottom of the siding line up to the top of the wall (the top plate or the bottom of the gable). Use one consistent height; if walls differ, run the calculator for each section.

Gable Triangles

A gable is the triangle under the roof peak. Its area is half the base width times the vertical height. The base width usually equals the building width, and the height is the rise from the wall top to the peak.

To double-check a complex shape, break it into rectangles and triangles and use the square footage calculator to total the parts.

You do not side over doors and windows, so their area is subtracted. The waste factor then adds material back for the real-world cuts.

Door and Window Allowances

This tool uses 21 sq ft per door (a standard 3 ft x 7 ft door) and 12 sq ft per window as an average. Large picture windows or sliding doors cover more, so for those count extra openings or raise the window area in your head before entering the count.

Choosing a Waste Factor

Ten percent suits a simple rectangular house. Raise it to 12 to 15 percent for many corners, dormers, angled walls or long diagonal cuts. Lower waste risks running short mid-job.

Why Round Up to Whole Squares

Siding is boxed and sold by the square, so suppliers round to whole squares. The calculator shows both the exact squares and the whole squares you will actually buy.

Planning a Re-side or New Build

Before ordering, get a material list so you buy the right number of squares and avoid return trips to the supplier.

Comparing Contractor Bids

Siding is quoted by the square. Knowing your square count lets you compare bids fairly and spot numbers that look too high or too low.

Budgeting a Project

Multiply squares by a price per square to set a material budget. Add trim, corners, fasteners and labor for a full picture.

Checking a Supplier Quote

Run your own numbers as a reference point when a supplier or estimator hands you a figure.

1. Forgetting the Gables

Gable triangles can add a surprising amount of area on a two-story or steep-roof house. Leaving them out leaves you short.

2. Subtracting Every Small Opening

Subtracting tiny windows exactly can make you under-order, because you still cut full pieces around them. The waste factor is there to cover this.

3. Skipping the Waste Factor

Every wall has cut-off pieces at corners and openings. Ordering the net area with no waste almost always runs short.

4. Mixing Up Perimeter and Area

Perimeter is the distance around the walls in feet; area is perimeter times height in square feet. Enter perimeter, not area, in the perimeter box.

5. Ignoring Product Coverage

Boxes of siding state the coverage per box. Convert your squares to boxes using that figure before you place the order.

The geometry is exact, but the openings and waste are typical allowances that you should adjust to your project.

Multiply the wall perimeter by the wall height for wall area, add the gable triangle areas, then subtract the area of doors and windows. Add a waste factor and divide by 100 to get squares.

A square is the industry unit for siding and equals 100 square feet of wall coverage. Vinyl, fiber cement and other siding are priced and packaged around the square.

A gable is the triangle under the roof peak. Its area is one half of the base width times the vertical height from the wall top to the peak. Multiply by the number of gables.

With 9 ft walls, two 24 by 6 ft gables, two doors, six windows and 10% waste, the net area is 1,110 sq ft, or about 13 squares after waste and rounding.

Yes, subtract their area because you do not side over them. This tool uses 21 sq ft per door and 12 sq ft per window, and the waste factor covers the cuts around them.

Ten percent is typical for a simple rectangular house. Use 12 to 15 percent for walls with many corners, dormers or angled sections.

Costs vary widely by product and region. Enter your own price per square to get an estimate; the tool multiplies it by the whole squares you need to order.

Siding is boxed and sold by the square, so suppliers round up. The tool shows the exact squares too, but you order whole squares to avoid running short.

Yes. The square footage is the same for any siding product. Check the coverage per box on your chosen product to turn squares into the number of boxes to buy.

The area math is exact. The door, window and waste values are typical allowances, so adjust them for large openings or complex walls and confirm all measurements on-site.

• Area of a rectangle and a triangle (Standard geometry: rectangle area is width times height; triangle area is one half base times height).
• ASTM building product and siding standards (ASTM International; material standards referenced for siding products and coverage).
• ICC International Residential Code - Wall Covering (International Code Council; residential code references for exterior wall coverings).