Avg Costs: Asphalt $100-$150, Metal $300-$600, Tile $600+
Base Floor Area:–
Pitch Multiplier:–
Actual Roof Area (incl. Slope):–
Total with Waste Factor:–
Roofing "Squares" Needed:–
Estimated Material Cost: –
function calculateRoofCost() {
// Get Inputs
var baseArea = parseFloat(document.getElementById('baseArea').value);
var pitchMultiplier = parseFloat(document.getElementById('roofPitch').value);
var wasteFactor = parseFloat(document.getElementById('wasteFactor').value);
var costPerSquare = parseFloat(document.getElementById('costPerSquare').value);
// Validation
if (isNaN(baseArea) || baseArea <= 0) {
alert("Please enter a valid base area in square feet.");
return;
}
if (isNaN(costPerSquare) || costPerSquare < 0) {
alert("Please enter a valid material cost per square.");
return;
}
// Calculations
// 1. Calculate area accounting for slope
var slopedArea = baseArea * pitchMultiplier;
// 2. Add waste factor
var totalAreaNeeded = slopedArea * wasteFactor;
// 3. Calculate "Squares" (1 square = 100 sq ft)
// We ceil to the nearest whole square because you can't buy partial bundles usually
// But for cost estimation, we can keep it decimal or ceil it. Let's ceil for realism.
var squaresNeeded = Math.ceil(totalAreaNeeded / 100);
// 4. Total Cost
var totalCost = squaresNeeded * costPerSquare;
// Display Results
document.getElementById('displayBaseArea').innerText = baseArea.toLocaleString() + " sq. ft.";
document.getElementById('displayPitch').innerText = "x" + pitchMultiplier;
document.getElementById('displayRoofArea').innerText = Math.round(slopedArea).toLocaleString() + " sq. ft.";
document.getElementById('displayTotalSqFt').innerText = Math.round(totalAreaNeeded).toLocaleString() + " sq. ft.";
document.getElementById('displaySquares').innerText = squaresNeeded + " Squares";
document.getElementById('displayTotalCost').innerText = "$" + totalCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show Result Box
document.getElementById('resultBox').style.display = "block";
}
How to Estimate Roofing Costs Effectively
Calculating the cost of a new roof involves more than just measuring the perimeter of your home. To get an accurate estimate, you must account for the roof pitch (steepness), the complexity of the design, and the inevitable material waste.
Understanding the "Square"
In the roofing industry, materials are rarely sold by the square foot. Instead, contractors and suppliers use the term "Square". One Square equals 100 square feet of roofing area. Our calculator automatically converts your total surface area into Squares to help you determine how many bundles of shingles or sheets of metal you need to purchase.
Why Pitch Matters
A common mistake when budgeting for a roof replacement is assuming the roof area equals the home's floor plan area. This is only true for completely flat roofs. As the roof gets steeper, the surface area increases significantly.
Low Pitch (4:12): Adds about 5.4% to your base area.
Medium Pitch (6:12): The industry standard, adding roughly 11.8% to the area.
Steep Pitch (12:12): A 45-degree angle roof, which increases the surface area by over 41%.
Accounting for Waste
You can never install roofing with 100% efficiency. Materials must be cut to fit valleys, hips, ridges, and edges. A simple gable roof might only require 5% waste allowance, while a complex roof with multiple dormers and intersecting angles often requires 10% to 15% extra material. This calculator includes these waste factors to ensure you don't run short on materials halfway through the project.
Average Material Costs per Square
When inputting your cost in the calculator above, consider these 2024 national averages: