Quick Calculators · Free to use
Roofing Calculator
Convert horizontal roof area to sloped coverage, squares, and whole bundles.
Your estimate
Enter your measurements to see the estimate.
Whole bundles with waste
bundles- Slope multiplier
- ×
- Sloped roof surface
- sq ft
- Surface with waste
- sq ft
- Roofing squares with waste
- squares
One roofing square is 100 sq ft. Product bundle coverage must be supplied.
Area estimate only, not roof design or code compliance. Measure roof planes separately when slopes differ. Hips, valleys, dormers, cuts, and other roof features require appropriate measurement and allowances.
How to Use This Calculator
Convert horizontal roof area to sloped coverage, squares, and whole bundles.
Decimals and fractions accepted for dimensions. Unmarked values use the labeled unit; explicit feet/inches are converted. For example, 10' 6 1/4" is an explicit length; 10.6 means 10.6 of the labeled unit. Rates, prices, counts and areas use numbers only.
Inputs and where to find them
Projected roof area (sq ft). Projected roof area is the roof’s footprint viewed straight down, including the overhangs you intend to cover. It is not the area measured along the sloping roof surface. Separate roof planes with different pitches so slope is applied correctly to each one.
Rise per 12 in of run (in). Pitch describes how many inches the roof rises for every 12 inches of horizontal travel. Obtain it from the plans or a level measurement. Enter only the rise, such as 5 for a 5:12 pitch; leaving it blank applies no slope increase.
Waste allowance (%). Enter the percentage you want to add for cutting, handling loss or other conditions specific to this work. Apply it to the measured quantity rather than enlarging the measurements as well. The suggested value is editable, not a universal recommendation; enter zero when no allowance is needed.
Bundles per roofing square. A roofing square is 100 square feet of roof area. Enter the number of bundles your selected shingle product requires to cover one square. Check the packaging or supplier information rather than assuming every shingle uses the same bundle count.
Results, example and assumptions
The slope factor converts the footprint to sloped roof area. Required area then adds waste, roofing squares express that area in 100-square-foot units, and bundles round the selected product’s requirement upward. These results do not separately count starter strips, ridge caps, flashing or underlayment.
Slope factor = √(12² + rise²) ÷ 12.
Sloped area = projected area × slope factor.
Required area = sloped area × (1 + waste ÷ 100).
Squares = required area ÷ 100.
Bundles = round up(squares × bundles per square).
Worked example: For 1,200 sq ft projected area at 5:12 pitch, the slope factor is 13 ÷ 12. Sloped area is 1,300 sq ft. With 10% waste, allow 1,430 sq ft or 14.3 squares. If your product requires 3 bundles per square, 42.9 rounds up to 43 bundles.
Area estimate only, not roof design or code compliance. Measure roof planes separately when slopes differ. Hips, valleys, dormers, cuts, and other roof features require appropriate measurement and allowances.