Roof Area Calculator
Sloped area and edge lengths, from a preset roof or plane by plane.
Roof
= 480" (40')
= 336" (28')
= 18" (1' 6")
= 12" (1')
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Roof Area · Result
CalculatedROOF AREA
14.56 squares
- Sloped area
- 1455.68 ft²
- Plan area
- 1302 ft²
- Ridge + hips
- 42.0 ft
- Eaves
- 84.0 ft
Code references & assumptions · 1
How this result is supported
- ASSUMPTIONSloped area is plan area (including overhangs) times the slope factor; a gable and a hip over the same footprint have the same sloped area and different edges
- ASSUMPTION
What do these evidence labels mean?
- PRIMARY-VERIFIED
- directly supported by one authoritative primary source, quoted with section/page/figure
- CROSS-VERIFIED
- independently supported by two or more appropriate authoritative sources
- DERIVED
- mathematically derived from PRIMARY-VERIFIED values; the derivation is preserved in data and in code
- INTERPRETED
- a source exists but translating it into calculator behaviour required interpretation
- CONVENTION
- recognised trade practice, not a mandatory provision
- ASSUMPTION
- product/design assumption or useful default with no authoritative basis
- UNVERIFIED
- insufficient authoritative evidence
Code references and product data are quoted in the units their source uses.
Reference checks are informational, not compliance determinations.
How roof area is calculated
Area is measured along the slope, not on the plan, so the plan area is multiplied by the slope factor for the pitch. Overhangs are added to the footprint first, because a roof is larger than the building under it.
The preset forms — gable, hip, shed and flat — cover most simple roofs from a length, a width and a pitch. Anything else is entered plane by plane as horizontal projections, which is what a plan actually gives you, and each plane can carry its own pitch.
Edge lengths come back with the area because a takeoff needs both. The eaves take drip edge and starter, the rakes take drip edge, and the ridge and hips take cap — and a hip roof's cap run is more than double a gable's over the same footprint.
sloped area = plan area × slope factor
squares = sloped area ÷ 100
hip length = plan run × hip and valley factor