Roof Area Calculator
A roof area calculator finds the true surface area of your roof by taking the building footprint and multiplying by the pitch factor, since a sloped roof covers more area than the ground beneath it. Enter your footprint dimensions and roof pitch below to get the roof area in square feet and roofing squares.
Enter footprint dimensions to see the roof area.
How Do You Calculate Roof Area?
To calculate roof area, find the building footprint (length times width of the area under the roof), then multiply by the pitch multiplier to get the true sloped area. A 40 by 30 foot footprint is 1,200 square feet flat; at a 6:12 pitch the real roof area is about 1,344 square feet. Divide by 100 for roofing squares. The calculator applies the correct multiplier for your pitch automatically.
Why Is Roof Area Bigger Than the Footprint?
Roof area is bigger than the footprint because the roof slopes, so each section of roof is the hypotenuse of a triangle whose base is the footprint. The steeper the pitch, the longer that slope and the bigger the area. This is why you cannot just use the building's floor area to order roofing: you must apply the pitch multiplier, which the calculator does for you.
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Frequently asked questions
- How do I calculate roof area?
- Multiply the building footprint by the pitch multiplier. A 1,200 square foot footprint at 6:12 pitch is about 1,344 square feet of roof, or 13.4 squares.
- Why is roof area larger than the house footprint?
- Because the roof slopes, each section is longer than its footprint base. Steeper pitches mean larger roof area, set by the pitch multiplier.