Estimating the correct amount of siding for your home is crucial for any renovation or new construction project. Ordering too little can cause delays and additional shipping costs, while ordering too much leads to unnecessary expenses and waste. Our Siding Square Footage Calculator helps you accurately determine the material needed, accounting for walls, gables, and deductions for windows and doors, plus a recommended waste factor.
How to Measure for Siding
To use this calculator effectively, you'll need a few key measurements from your home:
Total Wall Length: Measure the length of each exterior wall and sum them up. For a rectangular house, this would be (Length1 + Length2 + Length3 + Length4).
Average Wall Height: Measure the height of your walls from the foundation to the eaves. If heights vary, take an average.
Window Dimensions: Count the number of windows and measure their average width and height.
Door Dimensions: Count the number of doors and measure their average width and height.
Gable Dimensions: For triangular gable ends (often found on the ends of a house under a pitched roof), measure the base (the width of the house at the eaves) and the height (from the base to the peak of the roof).
Waste Factor: This is an additional percentage added to account for cuts, mistakes, and damaged pieces. A typical waste factor is 5-15%, depending on the complexity of the house and the siding material.
Understanding the Calculation
The calculator works by first determining the total surface area of your walls and gables. Then, it subtracts the areas of all windows and doors, as these sections will not be covered by siding. Finally, it applies a waste factor to ensure you have enough material for the job.
Main Wall Area: Total Wall Length × Average Wall Height
Gable Area: 0.5 × Gable Base × Gable Height (for each gable)
Window Area: Average Window Width × Average Window Height (for each window)
Door Area: Average Door Width × Average Door Height (for each door)
Net Siding Area: (Main Wall Area + Total Gable Area) – (Total Window Area + Total Door Area)
Final Siding Square Footage: Net Siding Area × (1 + Waste Factor / 100)
Example Calculation
Let's say you have a house with the following dimensions:
Total Wall Length: 120 feet
Average Wall Height: 10 feet
Number of Windows: 12
Average Window Width: 3 feet
Average Window Height: 4 feet
Number of Doors: 3
Average Door Width: 3 feet
Average Door Height: 7 feet
Number of Gables: 2
Average Gable Base: 30 feet
Average Gable Height: 8 feet
Waste Factor: 10%
Using the calculator:
Main Wall Area: 120 ft * 10 ft = 1200 sq ft
Total Window Area: 12 * 3 ft * 4 ft = 144 sq ft
Total Door Area: 3 * 3 ft * 7 ft = 63 sq ft
Total Gable Area: 2 * 0.5 * 30 ft * 8 ft = 240 sq ft
Gross Area (Walls + Gables): 1200 sq ft + 240 sq ft = 1440 sq ft
Openings Area (Windows + Doors): 144 sq ft + 63 sq ft = 207 sq ft
Net Siding Area: 1440 sq ft – 207 sq ft = 1233 sq ft
Final Siding Square Footage (with 10% waste): 1233 sq ft * (1 + 10/100) = 1233 sq ft * 1.10 = 1356.3 sq ft
You would need approximately 1356.3 square feet of siding.
Window Deductions
Door Deductions
Gable Ends (Triangular Sections)
function calculateSidingSqFt() {
// Get input values
var totalWallLength = parseFloat(document.getElementById('totalWallLength').value);
var averageWallHeight = parseFloat(document.getElementById('averageWallHeight').value);
var numWindows = parseFloat(document.getElementById('numWindows').value);
var avgWindowWidth = parseFloat(document.getElementById('avgWindowWidth').value);
var avgWindowHeight = parseFloat(document.getElementById('avgWindowHeight').value);
var numDoors = parseFloat(document.getElementById('numDoors').value);
var avgDoorWidth = parseFloat(document.getElementById('avgDoorWidth').value);
var avgDoorHeight = parseFloat(document.getElementById('avgDoorHeight').value);
var numGables = parseFloat(document.getElementById('numGables').value);
var avgGableBase = parseFloat(document.getElementById('avgGableBase').value);
var avgGableHeight = parseFloat(document.getElementById('avgGableHeight').value);
var wasteFactor = parseFloat(document.getElementById('wasteFactor').value);
// Validate inputs
if (isNaN(totalWallLength) || totalWallLength < 0 ||
isNaN(averageWallHeight) || averageWallHeight < 0 ||
isNaN(numWindows) || numWindows < 0 ||
isNaN(avgWindowWidth) || avgWindowWidth < 0 ||
isNaN(avgWindowHeight) || avgWindowHeight < 0 ||
isNaN(numDoors) || numDoors < 0 ||
isNaN(avgDoorWidth) || avgDoorWidth < 0 ||
isNaN(avgDoorHeight) || avgDoorHeight < 0 ||
isNaN(numGables) || numGables < 0 ||
isNaN(avgGableBase) || avgGableBase < 0 ||
isNaN(avgGableHeight) || avgGableHeight < 0 ||
isNaN(wasteFactor) || wasteFactor < 0) {
document.getElementById('sidingResult').innerHTML = 'Please enter valid positive numbers for all fields.';
return;
}
// Calculate main wall area
var mainWallArea = totalWallLength * averageWallHeight;
// Calculate total window area
var totalWindowArea = numWindows * avgWindowWidth * avgWindowHeight;
// Calculate total door area
var totalDoorArea = numDoors * avgDoorWidth * avgDoorHeight;
// Calculate total gable area (Area of a triangle = 0.5 * base * height)
var totalGableArea = numGables * 0.5 * avgGableBase * avgGableHeight;
// Calculate gross area (walls + gables)
var grossArea = mainWallArea + totalGableArea;
// Calculate total area of openings (windows + doors)
var openingsArea = totalWindowArea + totalDoorArea;
// Calculate net siding area
var netSidingArea = grossArea – openingsArea;
// Ensure net siding area is not negative
if (netSidingArea < 0) {
netSidingArea = 0; // Cannot have negative siding area
}
// Apply waste factor
var finalSidingSqFt = netSidingArea * (1 + wasteFactor / 100);
// Display result
document.getElementById('sidingResult').innerHTML =
'