Roof Area Calculator
From the building footprint and the roof pitch to the true sloped roof area, using the pitch multiplier — in square feet, square meters and roofing squares.
The roof is bigger than the house under it
A roof's true area is not the building's footprint — the slope stretches it. Estimators bridge the two with the pitch multiplier: the slope factor for the roof's pitch, applied to the flat footprint. This calculator takes the footprint (eaves included — measure the roof's outline, not the walls) and the pitch, and returns the true area in square feet, square meters and roofing squares, for a gable or a hip roof.
Pitch multiplier = √(1 + (pitch ÷ 12)²) · Roof area = footprint × multiplier · 1 roofing square = 100 sq ft
Example: a 40 × 30 ft footprint under a 6/12 pitch: the multiplier is 1.118, so the roof is 1,341.64 sq ft — 13.42 squares — though the house under it is only 1,200 sq ft.
Why gable and hip come out equal
| Pitch | Multiplier | Pitch | Multiplier |
|---|
| 3/12 | 1.031 | 8/12 | 1.202 |
| 4/12 | 1.054 | 9/12 | 1.250 |
| 5/12 | 1.083 | 10/12 | 1.302 |
| 6/12 | 1.118 | 12/12 | 1.414 |
At the same pitch, a hip roof and a gable roof over the same footprint have the same sloped area — every square foot of footprint is covered by slope stretched by the same factor; the hip trades two gable triangles of wall for two more roof facets. What changes is the ridge: a gable's ridge runs the building's length, while a hip's ridge is shorter by roughly the building's width — shown on the result because ridge cap is ordered by the foot. Dormers, valleys and intersecting wings break the one-pitch rule: measure those roofs facet by facet, or use the footprint of each wing with its own pitch and add.
This is the area the material calculators consume: the roofing calculator turns it into squares, bundles and rolls, and the metal roofing calculator into panels and screws.
Frequently asked questions
How do I find my roof's pitch without climbing?
From the attic against a rafter with a level and tape, from a pitch app held to the roof edge, or estimated from the ground: rise over run of the gable triangle. The roof pitch calculator converts any two of pitch, angle and percent — and a wrong pitch by 1/12 only moves the area by about 1–2%.
Should the footprint include the eaves overhang?
Yes — the roof covers the overhang, so measure the roof's outline from the ground (or add twice the overhang to the wall dimensions). A 1 ft overhang on a 40 × 30 house makes the roof footprint 42 × 32 ft, about 12% more area than the walls alone.
How many squares is my roof?
Roofing squares are just hundreds of square feet: divide the true roof area by 100. 1,341.64 sq ft is 13.42 squares. Shingles are quoted, bundled and warranted in squares — the roofing calculator finishes that step.
Does a steeper roof really cost proportionally more?
In material, yes — at 12/12 the roof carries 41% more shingle than its footprint. In labor, more than proportionally: steep roofs are slower and harder to work. The area figure here is the material truth both prices start from.
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