Loona Construction Calculators
Enter a roof's rise and run — in metres, feet, centimetres or inches, the ratio is the same — and get everything at once: the pitch ratio in x-in-12 form, the slope angle in degrees, the grade as a percentage, and the rafter (slope) length for your run.
About 18.4°. Common conversions: 3-in-12 = 14.0°, 6-in-12 = 26.6°, 9-in-12 = 36.9°, 12-in-12 = 45°. The angle is the arctangent of rise ÷ run.
It depends on the covering: standard concrete tiles typically need at least 22.5°, plain tiles 35°, slates 25–30°, while metal sheeting and membranes can go much lower. Always check the manufacturer's limit for your exact product.
From inside the attic or off a ladder at the gable: hold a level 12 inches (or 30 cm) horizontally from the roof surface and measure the vertical distance down to the roof — that is your rise per 12 (or per 30 cm, scaled).
Pitch (x-in-12) = Rise ÷ Run × 12
Angle = arctan(Rise ÷ Run), in degrees
Grade = Rise ÷ Run × 100%
Rafter length = √(Rise² + Run²) — Pythagoras on the slope triangle
North American roofing expresses pitch as inches of rise per 12 inches of run; most of the rest of the world uses the angle or the percentage. This calculator shows all three.
No. Pitch is a ratio of two lengths in the same unit, so metres, feet, centimetres or inches all give the same pitch, angle and grade. Only the rafter length follows the unit you entered.
Above about 9-in-12 (36.9°) is considered steep — harder and slower to work on. 4-in-12 to 9-in-12 is the conventional range for houses; below 4-in-12 is low-slope and needs coverings rated for it.
Take the rafter length for your full run, then add the eaves overhang (measured along the slope) and a little extra for the ridge cut and trimming. This calculator gives the pure slope length between the two measured points.
Add this calculator to your own website or blog — it is completely free, needs no sign-up, and always shows the latest version. Copy the code below and paste it into your page where you want the calculator to appear. Keeping the small “Powered by Loona Automation” credit line under the embed helps keep this tool free — but you are free to style or remove it; the tool works either way.