function calculateRoof() {
var length = parseFloat(document.getElementById('roofLength').value);
var width = parseFloat(document.getElementById('roofWidth').value);
var pitchMultiplier = parseFloat(document.getElementById('roofPitch').value);
var materialPrice = parseFloat(document.getElementById('materialType').value);
var waste = parseFloat(document.getElementById('wasteFactor').value);
if (isNaN(length) || isNaN(width) || isNaN(waste) || length <= 0 || width <= 0) {
alert("Please enter valid dimensions for the roof.");
return;
}
// Base area
var baseArea = length * width;
// Actual surface area adjusted for pitch
var actualSurfaceArea = baseArea * pitchMultiplier;
// Area including waste factor
var totalAreaWithWaste = actualSurfaceArea * (1 + (waste / 100));
// Roofing "Squares" (1 square = 100 sq ft)
var squares = totalAreaWithWaste / 100;
// Total Cost
var totalCost = totalAreaWithWaste * materialPrice;
// Display Results
document.getElementById('resArea').innerText = actualSurfaceArea.toFixed(0) + " sq. ft.";
document.getElementById('resSquares').innerText = squares.toFixed(2) + " squares";
document.getElementById('resTotalArea').innerText = totalAreaWithWaste.toFixed(0) + " sq. ft.";
document.getElementById('resCost').innerText = "$" + totalCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('roofResult').style.display = 'block';
}
How to Calculate Roofing Materials and Costs
Replacing a roof is one of the most significant investments a homeowner can make. Understanding the metrics used by contractors helps you budget effectively and compare quotes with confidence. Our roofing calculator simplifies the complex math involving pitch, squares, and waste factors.
Understanding "Roofing Squares"
In the roofing industry, the term "Square" is the standard unit of measurement. One roofing square equals 100 square feet of roof surface. For example, if your roof's total surface area is 2,400 square feet, your contractor will refer to it as 24 squares.
The Importance of Roof Pitch
Roof pitch is the steepness of your roof, expressed as a ratio of "rise over run." A 4/12 pitch means the roof rises 4 inches for every 12 inches it runs horizontally. The steeper the pitch, the more surface area the roof has compared to the building's footprint. Our calculator uses a pitch multiplier (the square root of (rise² + run²) / run) to ensure accuracy.
Factoring in Waste
No roofing project uses exactly the amount of material that matches the surface area. Shingles must be trimmed at valleys, hips, and edges.