';output += 'Area with Waste (' + WS + '%): ' + totalAreaWithWaste.toFixed(2) + ' sq. ft.
';output += '
';if(!isNaN(CS)){output += 'Estimated Material Cost: $' + materialCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});}if(document.getElementById('steps').checked){output += '
';output += 'Step-by-Step Breakdown:
';output += '1. Base Area including overhangs: (' + L + ' + ' + (2*O) + ') × (' + W + ' + ' + (2*O) + ') = ' + groundArea.toFixed(2) + ' sq. ft.
';output += '2. Adjust for Pitch (' + P + ' multiplier): ' + groundArea.toFixed(2) + ' × ' + P + ' = ' + actualRoofArea.toFixed(2) + ' sq. ft.
';output += '3. Add ' + WS + '% waste: ' + actualRoofArea.toFixed(2) + ' + ' + wasteAmount.toFixed(2) + ' = ' + totalAreaWithWaste.toFixed(2) + ' sq. ft.
';output += '4. Convert to Squares (Area ÷ 100): ' + totalAreaWithWaste.toFixed(2) + ' ÷ 100 = ' + squares.toFixed(2) + ' squares.';}output += '
How to Use the Roofing Calculator
Planning a roofing project requires precision to ensure you order the right amount of shingles, underlayment, and drip edge. Our roofing calculator simplifies this process by accounting for house dimensions, roof pitch, and waste factors. To get started, follow these steps:
- House Length and Width: Enter the horizontal footprint of your house.
- Roof Pitch: Select the slope of your roof. This is critical because a steeper roof has a larger surface area than a flat one for the same footprint.
- Eave Overhang: Most roofs extend past the walls. Enter the distance (usually 1 to 2 feet) to include this area in the calculation.
- Waste Factor: Standard practice suggests adding 10-15% for cuts, hips, and valleys.
Understanding Roofing Units: What is a "Square"?
In the roofing industry, materials are measured in "squares." One square of roofing is equal to 100 square feet of roof surface. This roofing calculator automatically converts your total square footage into squares, which is the unit used when buying shingles or hiring contractors.
Shingles are typically sold in bundles. For standard 3-tab or architectural shingles, it takes 3 bundles to cover 1 square. If your calculator result shows 20 squares, you will need at least 60 bundles of shingles.
The Mathematical Formula
To determine your roof size manually, we use the following formula:
Total Area = (Ground Area × Pitch Multiplier) + Waste Factor
The "Pitch Multiplier" is derived from the Pythagorean theorem. For example, a 6/12 pitch means the roof rises 6 inches for every 12 inches of run. This creates a slope factor of approximately 1.118.
Roofing Calculation Example
Scenario: You have a ranch-style home that is 50 feet long and 30 feet wide. The roof has a 1.5-foot overhang and a standard 4/12 pitch.
- Calculate Ground Area: (50 + 3) × (30 + 3) = 53 × 33 = 1,749 sq. ft.
- Apply Pitch Multiplier (4/12 = 1.054): 1,749 × 1.054 = 1,843.45 sq. ft.
- Add 10% Waste: 1,843.45 × 1.10 = 2,027.80 sq. ft.
- Convert to Squares: 2,027.80 / 100 = 20.28 Squares.
- Result: You should order 21 squares or 63 bundles of shingles.
Common Roofing Questions
How many bundles are in a square?
Most asphalt shingles come in 3 bundles per square. However, some heavy-weight designer shingles may require 4 or 5 bundles to cover one square (100 sq. ft.) due to their thickness and weight.
What waste factor should I use?
For a simple gable roof, 10% is usually sufficient. For complex roofs with many hips, valleys, dormers, and chimneys, you should use a waste factor of 15% to 20% to account for the extra cuts required.
Does roof pitch affect the price?
Yes, in two ways. First, a higher pitch increases the surface area, requiring more materials. Second, roofs with a pitch steeper than 7/12 often require specialized safety equipment and more labor time, which increases the installation cost per square.