Roof area calculator
Enter the plan length and width including overhangs and the pitch to get the area to cover.
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How to use it
- Enter plan length incl. overhang, plan width incl. overhang, pitch format, pitch and waste allowance.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Roof area = length × width ÷ cos(pitch angle). For pitch in 12: angle = arctan(pitch ÷ 12). 1 ft² = 0.09290304 m²; one roofing square = 100 ft².
Example
Inputs: Plan length incl. overhang = 12 m, Plan width incl. overhang = 8 m, Pitch format = Rise in 12, Pitch = 6, Waste allowance = 10 %. Result: Roof area: 107.33 m²; In square feet: 1,155 ft²; Roofing squares (100 ft²): 11.55.
Limits and caveats
- Valid for any roof whose planes share one pitch (gable or hip); roofs with mixed pitches need each part done separately.
- Openings such as skylights and chimneys are not subtracted.
Questions about this tool
Why use the plan area?
It is easier and safer to measure from the ground, and dividing by the cosine of the angle gives the exact sloped area when the pitch is uniform.
What is a roofing square?
A common roofing trade unit equal to 100 square feet, about 9.29 m².
How much waste should I add?
About 10% for simple gable roofs; hip roofs with many cuts may need 15% or more.