Free Tools
Roof Pitch & Rafter Length Calculator
Calculate pitch angle, ridge height, rafter length, and sloped roof area from span and building length. Free, with pitch tips per covering.
Note
This is a geometry/comfort calculation for early planning. The supporting structure (e.g. stair frame, roof trusses) still needs professional design.
Roof geometry result
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How to calculate roof pitch
Geometry from span & angle
From span width and pitch angle, the calculator computes ridge height = ½ span × tan(angle), rafter length = ½ span ÷ cos(angle), and sloped roof area = (span ÷ cos(angle)) × building length.
Pitch follows the covering
Clay tiles need a steeper pitch (30–40°) to keep water out, concrete tiles 25–35°, while metal can be flatter (10–25°). Pick a covering to get a suitable pitch recommendation.
Sloped roof is always larger
Because it slopes, the real roof area is larger than the plan area. The steeper the angle, the larger the area and rafter length needed — and the more frame and covering material required.
FAQ
Frequently asked questions
What's the ideal roof pitch for tiles?
Clay tiles generally need 30–40°, concrete tiles 25–35°, and metal 10–25°. Enough pitch matters so rain flows and doesn't seep. The calculator suggests a range for the covering type you pick.
How do I calculate rafter length?
Rafter length (support to ridge, half the sloped span) = ½ span width ÷ cos(angle). For an 8 m span at 30°, rafter length ≈ 4.6 m. Add overhang per your design if needed.
How do I calculate the real roof area?
Sloped roof area = (span width ÷ cos(angle)) × building length. This is always larger than the plan area because the roof slopes, and it matters for estimating tile and frame needs.
How does ridge height relate to pitch?
Ridge height = ½ span width × tan(angle). The steeper the angle, the higher the ridge. This is useful for designing attic-space height or a sloped ceiling.
Does this calculate roof material needs?
This page focuses on geometry (angle, rafter, area). To calculate light steel bars, battens, and tiles, use the light steel roof calculator which takes roof area and pitch. A link is provided in the result.
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