Roof Area Calculator
Calculate the sloped surface area of a gable or shed roof from building length, width, roof pitch, and overhangs. Get roof angle, slope percentage, roof multiplier, sloped roof length, plan area, total roof surface area, and roofing squares instantly.
Enter Roof Dimensions
Choose the roof type and provide its measurements.
What Is a Roof Area Calculator?
A roof area calculator estimates the actual sloped surface area of a roof rather than simply using the building's horizontal floor dimensions. Roof pitch increases the surface area because the roofing material follows the slope.
This calculator supports simple symmetrical gable roofs and single-slope shed roofs. It also lets you include eave and end overhangs so the estimated roofing surface better reflects the full roof footprint.
How to Use the Roof Area Calculator
Choose Roof Type
Select a gable roof with two equal slopes or a shed roof with one continuous slope.
Enter Dimensions
Provide building length, width, roof pitch, eave overhang, end overhang, and measurement unit.
Calculate Area
The tool calculates sloped roof area, roof multiplier, angle, roofing squares, and optional waste-adjusted area.
How Is Roof Area Calculated?
Roof Slope Multiplier
The pitch multiplier converts horizontal roof run into sloped roof length. For a roof with pitch X:12: Multiplier = √(1 + (X ÷ 12)²) .
Gable Roof Area
A simple gable roof contains two equal rectangular roof planes. The calculator finds the horizontal run from eave to ridge, converts it to sloped length, and multiplies it by the total roof length: Area = 2 × Slope Length × Roof Length .
Shed Roof Area
A shed roof contains one main sloped plane. Its full horizontal span is converted to sloped length using the roof multiplier: Area = Slope Length × Roof Length .
Common Roof Pitch Multipliers
| Pitch | Angle | Slope | Approx. Multiplier |
|---|---|---|---|
| 2:12 | 9.46° | 16.67% | 1.0138 |
| 3:12 | 14.04° | 25% | 1.0308 |
| 4:12 | 18.43° | 33.33% | 1.0541 |
| 5:12 | 22.62° | 41.67% | 1.0833 |
| 6:12 | 26.57° | 50% | 1.1180 |
| 8:12 | 33.69° | 66.67% | 1.2019 |
| 10:12 | 39.81° | 83.33% | 1.3017 |
| 12:12 | 45° | 100% | 1.4142 |
What Is a Roofing Square?
In roofing work using square feet, one roofing square represents 100 square feet of roof surface. For example, a 2,500 square-foot roof equals 25 roofing squares before adding waste.
The calculator displays roofing squares when feet are selected. For metric and other units, it continues to show the calculated area in the selected squared unit.
Roof Complexity Can Change the Required Material
This calculator estimates simple gable and shed roof geometry. Dormers, valleys, hips, intersecting roofs, curved sections, chimneys, skylights, and other roof features can change the actual material quantity.
For purchasing roofing materials, confirm measurements on the actual structure and follow the roofing manufacturer's coverage and installation requirements.