Calculate roof pitch angle, rafter length, and roof area from rise and run measurements. Convert between pitch ratio (x:12), degrees, and percentage. Essential for roofing estimates.
Roof pitch is the ratio of vertical rise to horizontal run. A 6:12 pitch means the roof rises 6 inches for every 12 inches of horizontal run, equal to a 26.6 degree angle.
Divide rise by run, then take the arctangent. For a 6:12 pitch: arctan(6/12) = arctan(0.5) = 26.57 degrees.
In India, 30 degree pitch is common for RCC roofs. In the UK and US, 6:12 to 8:12 (26.6-33.7 degrees) is standard for residential roofs. Low-pitch roofs are below 4:12 (18.4 degrees).
Use Pythagoras theorem: Rafter = square root of (Rise squared + Run squared). For rise=2m, run=4m: rafter = sqrt(4+16) = sqrt(20) = 4.47m.
Corrugated sheet roofing needs a minimum 5 degree (1:12) pitch. Clay tiles need 25-35 degrees. Flat roofs (0-5 degrees) need waterproof membranes and drainage design.
Steeper roofs need more material. A 12:12 pitch roof has 41% more surface area than a flat roof of the same plan area. Use a roof area calculator to account for this in material estimates.