Find the true sloped area of a roof. This free roof area calculator scales the building footprint by the pitch (degrees or rise:12) to give roof surface area, roofing squares and material bundles.
Roof footprint
m
m
m²
°
: 12
Enter the building’s plan footprint and the roof pitch (as an angle or a rise:12 ratio). The calculator scales the footprint by the slope to give the true roof surface area.
Roof area (sloped)
—
Enter footprint & pitch
Footprint
—
Slope factor
—
Roofing squares
—
Bundles
—
Sloped roof area = plan footprint × slope factor, where slope factor = 1 ÷ cos(pitch). A steeper roof has more surface than its footprint. “Roofing squares” are 100 ft² units used to order materials; add overhangs and waste separately.
Use this free roof area calculator to find the true sloped area of a roof. Enter the building footprint and the pitch to get the roof surface area, squares and material estimate.
What this roof area calculator does
A roof area calculator scales your flat footprint by the roof’s pitch to give the real sloped surface area — the area you actually need to cover with roofing material.
How roof area is calculated
slope factor = 1 ÷ cos(pitch)
roof area = footprint area × slope factor
So a 96 m² footprint at a 30° pitch has a roof area of about 111 m² — steeper roofs have proportionally more surface.
Pitch and slope factor
Pitch
Rise : 12
Slope factor
18.4°
4 : 12
1.054
26.6°
6 : 12
1.118
33.7°
8 : 12
1.202
45°
12 : 12
1.414
Footprint vs roof area
The footprint is the building’s plan area as seen from above; the roof area is larger because the surface slopes. Order materials by roof area, and add extra for overhangs, ridges, valleys and waste.
How to use the roof area calculator
Enter footprint size or area.
Set the pitch in degrees or as a rise:12 ratio.
Read the roof area and roofing squares.
Roof Area FAQ
How do I calculate roof area?
Multiply the building's footprint area by the slope factor, which is 1 ÷ cos(pitch). A 96 m² footprint at 30° gives about 111 m² of roof.
What is a roof slope factor?
It's how much bigger the sloped surface is than the flat footprint. At 6:12 it's about 1.118, and at 45° (12:12) it's 1.414.
What does a pitch like 6:12 mean?
The roof rises 6 units for every 12 units of horizontal run — that works out to about a 26.6° angle.
What is a roofing square?
A roofing square is 100 square feet, the unit used to order materials like shingles. Roof area in ft² ÷ 100 gives the number of squares.
Does this include overhangs and complex roofs?
It estimates a simple sloped roof. Add extra for overhangs, hips, valleys and waste, or measure a complex roof in sections.
Is the roof area calculator free?
Yes, this roof area calculator is completely free, needs no sign-up, and gives instant results in your browser.
