Calculating the total square footage of siding needed for your home is a crucial step in any exterior renovation project. It helps in accurately estimating material costs, ordering the right quantity of siding, and ensuring efficient installation. This calculator simplifies that process by taking into account the dimensions of your walls and the areas that will not be covered by siding, such as windows and doors.
The Math Behind the Calculation
The core of the siding square footage calculation involves determining the total surface area of the walls and then subtracting the areas of openings like windows and doors. A waste factor is then added to account for cuts, errors, and material unusable due to damage or defects.
Here's the breakdown of the calculation steps:
Calculate the area of each wall: For each wall, multiply its height by its width.
Calculate the total wall area: Sum the areas of all individual walls.
Calculate the area of each window: Multiply the height by the width of a single window.
Calculate the total window area: Multiply the area of a single window by the total number of windows.
Calculate the area of each door: Multiply the height by the width of a single door.
Calculate the total door area: Multiply the area of a single door by the total number of doors.
Calculate the net area: Subtract the total window area and total door area from the total wall area.
Add the waste factor: Calculate the amount of siding to add for waste and add it to the net area to get the final required square footage.
The formula used by this calculator is as follows:
Total Wall Area = Σ(Wall Height × Wall Width) Total Window Area = (Window Height × Window Width) × Number of Windows Total Door Area = (Door Height × Door Width) × Number of Doors Net Area to Cover = Total Wall Area – Total Window Area – Total Door Area Waste Amount = Net Area to Cover × (Waste Factor / 100) Total Siding Needed (sq ft) = Net Area to Cover + Waste Amount
Why Include a Waste Factor?
It's essential to order slightly more siding than the exact calculated area. This accounts for:
Cuts and Trim: Siding panels need to be cut to fit around corners, windows, doors, and other architectural features.
Mistakes: Accidental damage during handling or installation can occur.
Defects: Some pieces of siding may have manufacturing defects.
Variations: Odd angles or complex wall shapes may require more material.
A typical waste factor for siding ranges from 5% to 15%, depending on the complexity of the project and the type of siding.
Use Cases
This calculator is useful for:
Homeowners planning a DIY siding project.
Contractors providing estimates for siding installations.
Material suppliers helping customers determine quantities.
Renovation and remodeling professionals.
function calculateSidingArea() {
var wallHeight = parseFloat(document.getElementById("wallHeight").value);
var wallWidth = parseFloat(document.getElementById("wallWidth").value);
var numWindows = parseFloat(document.getElementById("numWindows").value);
var windowHeight = parseFloat(document.getElementById("windowHeight").value);
var windowWidth = parseFloat(document.getElementById("windowWidth").value);
var numDoors = parseFloat(document.getElementById("numDoors").value);
var doorHeight = parseFloat(document.getElementById("doorHeight").value);
var doorWidth = parseFloat(document.getElementById("doorWidth").value);
var wasteFactor = parseFloat(document.getElementById("wasteFactor").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "; // Clear previous results
// Input validation
if (isNaN(wallHeight) || wallHeight <= 0 ||
isNaN(wallWidth) || wallWidth <= 0 ||
isNaN(numWindows) || numWindows < 0 ||
isNaN(windowHeight) || windowHeight <= 0 ||
isNaN(windowWidth) || windowWidth <= 0 ||
isNaN(numDoors) || numDoors < 0 ||
isNaN(doorHeight) || doorHeight <= 0 ||
isNaN(doorWidth) || doorWidth <= 0 ||
isNaN(wasteFactor) || wasteFactor < 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Calculate total wall area
var totalWallArea = wallHeight * wallWidth;
// Calculate total window area
var totalWindowArea = (windowHeight * windowWidth) * numWindows;
// Calculate total door area
var totalDoorArea = (doorHeight * doorWidth) * numDoors;
// Calculate net area to cover
var netAreaToCover = totalWallArea – totalWindowArea – totalDoorArea;
// Ensure net area is not negative
if (netAreaToCover < 0) {
netAreaToCover = 0;
}
// Calculate waste amount
var wasteAmount = netAreaToCover * (wasteFactor / 100);
// Calculate total siding needed
var totalSidingNeeded = netAreaToCover + wasteAmount;
// Display the result
resultDiv.innerHTML = totalSidingNeeded.toFixed(2) + ' sq ft';
}