Calculating the square footage needed for siding is a crucial step in any exterior renovation project. It ensures you order the correct amount of material, minimizing waste and avoiding costly last-minute purchases. This calculator simplifies the process by taking into account the dimensions of your walls and subtracting areas that won't be covered by siding, such as windows and doors.
The Math Behind the Calculation
The fundamental principle is to calculate the total surface area of the walls and then subtract the areas of openings.
Total Wall Area: This is calculated by multiplying the height of a wall by its length, and then multiplying that by the total number of walls.
Total Wall Area = (Wall Height × Wall Length) × Number of Walls
Area of Openings: Windows and doors do not require siding. Their areas must be subtracted from the total wall area.
Total Opening Area = Total Window Area + Total Door Area
Net Siding Area: The final amount of siding needed is the total wall area minus the total area of openings.
Net Siding Area = Total Wall Area – Total Opening Area
Why This Matters
Accurate measurement is key for several reasons:
Cost Efficiency: Ordering too much material leads to unnecessary expense. Ordering too little can halt the project and incur extra shipping costs.
Material Ordering: Siding is often sold in specific quantities (e.g., by the square, where 1 square = 100 sq ft). Knowing your exact square footage helps you order the correct number of squares.
Waste Reduction: Proper planning minimizes offcuts and waste, contributing to a more sustainable project.
Example Calculation
Let's consider a house with the following dimensions:
Wall Height: 9 feet
Wall Length: 30 feet
Number of Walls: 4
Total Window Area: 40 sq ft
Total Door Area: 25 sq ft
Using our calculator or the formulas:
Total Wall Area = (9 ft × 30 ft) × 4 = 270 sq ft × 4 = 1080 sq ft
Total Opening Area = 40 sq ft + 25 sq ft = 65 sq ft
Net Siding Area = 1080 sq ft – 65 sq ft = 1015 sq ft
Therefore, you would need approximately 1015 square feet of siding for this house. It's often recommended to add an extra 5-10% for cuts, waste, and potential future repairs.
function calculateSidingArea() {
var wallHeight = parseFloat(document.getElementById("wallHeight").value);
var wallLength = parseFloat(document.getElementById("wallLength").value);
var numberOfWalls = parseFloat(document.getElementById("numberOfWalls").value);
var windowArea = parseFloat(document.getElementById("windowArea").value);
var doorArea = parseFloat(document.getElementById("doorArea").value);
var resultValueElement = document.getElementById("result-value");
// Clear previous results and error messages
resultValueElement.innerHTML = "–";
// Input validation
if (isNaN(wallHeight) || wallHeight <= 0) {
alert("Please enter a valid positive number for Wall Height.");
return;
}
if (isNaN(wallLength) || wallLength <= 0) {
alert("Please enter a valid positive number for Wall Length.");
return;
}
if (isNaN(numberOfWalls) || numberOfWalls <= 0) {
alert("Please enter a valid positive number for Number of Walls.");
return;
}
if (isNaN(windowArea) || windowArea < 0) {
alert("Please enter a valid non-negative number for Total Window Area.");
return;
}
if (isNaN(doorArea) || doorArea < 0) {
alert("Please enter a valid non-negative number for Total Door Area.");
return;
}
var totalWallArea = (wallHeight * wallLength) * numberOfWalls;
var totalOpeningArea = windowArea + doorArea;
var netSidingArea = totalWallArea – totalOpeningArea;
// Ensure the result is not negative (in case openings are larger than walls, though unlikely)
if (netSidingArea < 0) {
netSidingArea = 0;
}
resultValueElement.innerHTML = netSidingArea.toFixed(2) + " sq ft";
}