Roof Calculator
Calculate roof area: gable, hip, mansard roofs, slope angle. Online calculator for metal tile and corrugated sheet.
Length of the house along the ridge, in meters
Width of the house, in meters
Height from cornice to ridge, in meters
Overhang past the wall, typically 0.3–0.7 m
Calculation formula
S = √((W/2 + O)² + H²); A = 2 × (L + 2O) × S
Slope length S is the hypotenuse: half the width plus overhang as one leg, roof height as the other. Gable roof area equals two rectangles of length (L + 2 overhangs) and width S. Slope angle = arctan(H ÷ (W/2 + O)).
About the roof calculator
The roof calculator computes the area of a gable or hip roof from the house dimensions, ridge height and overhang length. It also returns the slope length and pitch angle — values you need when ordering metal tile, corrugated sheet, asphalt shingles or onduline.
The calculation is useful before buying roofing material: knowing the area lets you estimate the number of metal-tile or shingle sheets, the length of battens and rafters. The slope angle tells you whether your chosen material is suitable: every roofing product has its own minimum recommended pitch.
All math runs in your browser — nothing is sent to a server. The calculator is free, requires no sign-up, and has no usage limits.
Calculator benefits
Gable and hip
Two most common roof shapes for private houses — no manual formulas required.
Overhangs included
Overhang length is part of the formula, so the result is ready for ordering material with a margin.
Pitch in degrees
The slope angle is shown in degrees instantly — no need to compute the arctangent yourself.
FAQ
What is the optimal roof pitch?
For a private house in a temperate climate the optimal pitch is 25–45°: snow and water shed properly and the load on rafters stays moderate. In southern regions pitches from 15° are acceptable; in heavy-snow areas 35–60° works better.
What is the difference between gable and hip roofs?
A gable roof has two rectangular slopes and two vertical gable walls. A hip roof has four slopes: two trapezoidal sides and two triangular hips at the ends. The hip roof area is usually larger because of the end slopes.
What is the minimum pitch for metal tile?
Manufacturers recommend a minimum slope of 14° for metal tile. At lower pitches snow and water linger at the seams and leaks become almost inevitable. A pitch of 22° or more is considered optimal.
Should overhangs be included in the calculation?
Yes, always. Overhangs protect the walls and foundation from rain and need to be covered with roofing material. A typical overhang is 0.3–0.7 m on each side; the calculator defaults to 0.5 m.
How much extra material should I buy?
Add 5–10% to the calculated area for cuts and overlaps when using metal tile or corrugated sheet, and 10–15% for asphalt shingles and onduline. The more complex the roof shape, the larger the margin.
How accurate is the calculation?
The calculator uses a geometric model of a symmetrical gable roof and a pyramid-style hip roof. For asymmetric, multi-gable and mansard roofs the error can reach 10–15%, so a project drawing is preferable.