Calculation Results:
Base Area (with overhangs): 0 sq ft
Estimated Roof Surface: 0 sq ft
Total Area (with waste): 0 sq ft
Total Roofing Squares Required:
0
(1 Square = 100 Square Feet)
function calculateRoofing() {
var length = parseFloat(document.getElementById('houseLength').value);
var width = parseFloat(document.getElementById('houseWidth').value);
var pitchMultiplier = parseFloat(document.getElementById('roofPitch').value);
var overhang = parseFloat(document.getElementById('overhang').value);
var waste = parseFloat(document.getElementById('wasteFactor').value);
if (isNaN(length) || isNaN(width) || isNaN(overhang) || isNaN(waste)) {
alert("Please enter valid numeric values.");
return;
}
// Calculate area including the overhang on all sides
var totalLength = length + (overhang * 2);
var totalWidth = width + (overhang * 2);
var baseArea = totalLength * totalWidth;
// Apply the pitch multiplier
var surfaceArea = baseArea * pitchMultiplier;
// Apply waste factor
var totalWithWaste = surfaceArea * (1 + (waste / 100));
// Roofing Squares (100 sq ft = 1 square)
var squares = totalWithWaste / 100;
// Display Results
document.getElementById('resBaseArea').innerText = baseArea.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resSurfaceArea').innerText = surfaceArea.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resTotalArea').innerText = totalWithWaste.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resSquares').innerText = squares.toFixed(2);
document.getElementById('roofResult').style.display = 'block';
}
How to Calculate Roofing Square Footage
Calculating the amount of material needed for a new roof is critical for accurate budgeting. Roofing materials are sold by the "Square," which represents a 100-square-foot area. This calculator helps you convert ground-level measurements into actual sloped roofing surface area.
The Role of Roof Pitch
The "Pitch" or "Slope" of your roof significantly increases the surface area. A flat roof covering a 1,000-square-foot house is exactly 1,000 square feet. However, a steep 12/12 pitch roof covering that same house would require over 1,400 square feet of material because of the angle.
Why We Add a Waste Factor
No roofing project is perfect. You must account for shingles that are cut to fit valleys, hips, and gables. Standard guidelines suggest:
- 10%: Standard gable roofs (simple rectangles).
- 15%: Hip roofs or roofs with several dormers.
- 20%: Complex roofs with multiple valleys and high architectural detail.
Real-World Calculation Example
Imagine a standard rectangular ranch home:
- Footprint: 40 ft long by 30 ft wide.
- Overhang: 1.5 ft eaves on all sides.
- Pitch: 6/12 (Medium slope).
1. First, we calculate the area including overhangs: 43 ft x 33 ft = 1,419 sq ft.
2. We apply the 6/12 multiplier (1.118): 1,419 x 1.118 = 1,586.44 sq ft.
3. Adding 10% waste: 1,586.44 x 1.1 = 1,745.08 total sq ft.
4. Final result: 17.45 Squares (You would likely order 18 squares of shingles).
Pro Tip: Always remember to include separate measurements for detached garages or sheds if you intend to roof them at the same time to ensure color matching across shingle batches.