Roof area calculator
Slope area from the footprint and the pitch, in degrees or per cent.
Fill in the fields and the result will appear here automatically.
Works out the roof area from the footprint dimensions and the pitch. Worth knowing before you start: for any roof of constant pitch over the same footprint the area is the same — the footprint divided by the cosine of the angle. A single-slope, a gable and a hip roof differ not in the total but in how many planes it is split across, so the shape changes the breakdown rather than the sum. The pitch is given in degrees or as a percentage, and a percentage is converted through an arctangent rather than treated as an angle.
How it works
Formula and logic
Complete rectangular projection A₀ = L·W. If all slopes have the same pitch, A = A₀/cos α; percentage pitch p uses A = A₀·√(1 + (p/100)²) directly, without rounding p into an angle first. Degrees require 0 ≤ α < 90; percentage p is finite and nonnegative. A symmetric gable has A/2 on each side; hip mode reports four slopes without individual areas. Openings, unequal pitches and covering layout are not modeled.
Example
A gable roof over a 10 × 8 m footprint at a 30° pitch has an area of 92.376 m² — 46.188 m² per slope.
Fields and units
- Roof shape — list option
- Footprint length — m
- Footprint width — m
- How the pitch is given — list option
- Pitch — °
- Pitch — %
How to use
- — Choose the roof shape.
- — Enter the footprint length and width.
- — Give the pitch in degrees or as a percentage.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- This is a geometric quantity calculation within the described model. It does not establish load capacity, safety or project compliance; check design parameters separately.
FAQ
Why do a single-slope and a gable roof have the same area?
Because it depends only on the footprint and the pitch. A gable splits the same area across two slopes half the size — the sum does not change.
How does a percentage pitch differ from degrees?
A percentage is the rise over the run times a hundred. The angle follows through an arctangent: a 100 % pitch is 45°, not 90°.
Are the eaves included?
No. Enter the dimensions of the rectangle the roof actually covers, including the overhang if you want it counted.
Why is no per-slope area shown for a hip roof?
Because it depends on the ridge length, which is not asked for here. The total remains correct: it follows from the footprint and the pitch alone.