ConstructionCalc

Roof Square Footage Calculator: Area & Roofing Squares

Your roof’s surface in square feet and roofing squares, from the footprint, the overhang and the pitch, for a gable, hip or shed roof.

By Marko VisicBSc Physics, University of Ljubljana

1,503sq ft

of roof surface at 6/12

15.03 roofing squares

6/1242 ft32 ft
Footprint to the eaves
1,344 sq ft
Pitch multiplier
1.118
Roof angle
26.6°
Whole squares
16
In square meters
139.6 m²
Per 100 sq ft of footprint
111.8 sq ft

A roofing square is 100 sq ft of roof surface. Gable, hip or shed, a roof with one pitch on every plane has the same area over the same footprint. Not sure of the pitch? Find it with the roof pitch calculator.

Footprint
Units
Roof shape (for the drawing)

1,503 sq ft of roof, 15.03 squares

Roof area is the footprint out to the eaves times the pitch multiplier. A 40 by 30 ft house with 1 ft overhangs covers 1,344 sq ft in plan; at a 6/12 pitch that is 1,503 sq ft of roof, or 15.03 squares, since a roofing square is 100 sq ft.

Shingles, underlayment and roofing labor are all priced by the square, so the roof’s true surface matters more than the house’s floor area. You can get it from the ground: the outside dimensions of the walls, the overhang and the pitch are enough.

How to calculate roof square footage

Start with the footprint: the length times the width of the walls’ outside faces, each grown by the overhang on both sides. Then multiply by the pitch multiplier, the length along the roof for each unit of level run. That gives the surface the roofing actually covers.

Footprint to the eaves = (length + 2 × overhang) × (width + 2 × overhang)

Pitch multiplier = √(1 + (pitch ÷ 12)²)

Roof area = footprint × multiplier; squares = roof area ÷ 100

Example: walls 40 by 30 ft with 1 ft overhangs give a 42 by 32 ft footprint, 1,344 sq ft. At 6/12 the multiplier is 1.118, so the roof is 1,502.6 sq ft, 15.03 squares; rounded up, order for 16 squares before waste.

Why a hip roof has the same area as a gable

Each roof plane is its area in plan stretched by the same multiplier, because every plane tilts at the same angle. Add the planes and you get the whole footprint times the multiplier, whatever the roof’s shape. A hip and a gable over the same eaves at the same pitch have the same area.

Check: a hip over the same 42 by 32 ft footprint has two trapezoids of 416 sq ft and two triangles of 256 sq ft in plan, 1,344 sq ft in all, the same footprint as the gable. At 6/12 both roofs are 1,502.6 sq ft.

The rule breaks when parts of the roof have different pitches, as with a steep main roof and a low-slope porch, or when dormers add walls and cheeks. Work out each part with its own pitch, then add them.

Measuring without climbing the roof

Measure the house’s outside walls with a tape, then add the overhang: stand under an eave and measure from the wall to the roof edge. A satellite map with a distance tool works too, and because it sees the roof from above, its outline already includes the overhangs. Either way, the pitch is the one number you need from the roof itself, and the roof pitch calculator finds it from a level reading, an angle, or the building’s width and ridge height.

Rounding up to whole squares

Roofers count in squares: one square is 100 square feet of roof surface. Divide the roof area by 100, round up to a whole square, and add what the roofing maker or your roofer advises for cuts at hips, valleys and edges. How many bundles of shingles make a square depends on the product, so check the bundle’s printed coverage before you order.

The roof pitch chart lists the multiplier for every pitch from 1/12 to 24/12, which is handy for quick estimates by hand.

Roof area calculator FAQ

How many squares is my roof?

Divide the roof’s surface area by 100, since a roofing square is 100 square feet. A 40 by 30-foot house with 1-foot overhangs and a 6/12 roof has about 15.0 squares.

How do I calculate the area of a hip roof?

The same way as a gable: multiply the footprint out to the eaves by the pitch multiplier. Each hip plane is its plan area times the multiplier, so the four planes add up to the whole footprint times the multiplier, as long as they share one pitch.

How much bigger is a roof than the house?

By the pitch multiplier, plus the overhangs. At 6/12 the roof is 11.8% larger than its footprint to the eaves; at 12/12 it is about 41% larger.

Do overhangs count in roof square footage?

Yes. The roofing covers the overhangs too, so measure the footprint to the eaves, not to the walls. With a 1-foot overhang, a 40 by 30-foot house covers 1,344 square feet in plan instead of 1,200.

Sources & method

The area is geometry: the footprint to the eaves times the pitch multiplier, computed from the inputs. The square is the roofing industry’s unit, as Owens Corning and GAF define it.

  1. Owens Corning. DIY Roofing: Re-Roofing Tips (What is a “Roofing Square”?). page read Nov 14, 2026