Roof Triangle (to scale)
Diagram is illustrative based on your current rise/run. Not for code-compliance drawings.
Roof Pitch Calculator – Angle, Slope, Rafter Length & Area
This roof pitch calculator converts between pitch (rise in 12), angle in degrees, and slope percentage. Enter any one (or rise and run) and the tool solves the rest. For quick estimating, add your half-span and optional overhang to get a common rafter length. If you provide roof length and building span, it also estimates roof surface area for quoting underlayment, shingles, or metal sheets.
What Does Roof Pitch Mean?
In Imperial units, pitch is written as X-in-12 (e.g., 6/12 means the roof rises 6 inches for every 12 inches of run). In Metric, this calculator treats presets as rise per 1 meter of run for consistency.
Typical Roof Pitches
- Low slope: 2/12–4/12 (≈9.5°–18.4°)
- Common residential: 4/12–8/12 (≈18.4°–33.7°)
- Steep slope: 9/12+ (≈36.9°+)
How We Calculate
- Angle (°) = arctan(rise/run)
- Slope (%) = (rise/run) × 100
- Common rafter length = √(rise² + run²) for your half-span; with overhang, we extend the horizontal run and rise proportionally.
- Roof surface area = plan area ÷ cos(angle) = (roof length × span) ÷ cos(angle)
FAQs
Is pitch the same as angle?
No. Pitch is a ratio (e.g., 6/12). Angle is the arctangent of rise/run in degrees. The calculator shows both.
What do I enter for run?
If you’re working from a pitch like 6/12, you can leave run blank; the calculator assumes 12 inches (or 1 m in Metric) as the reference run.
How accurate is the area?
It’s an estimate for simple gable roofs. Complex roofs (hips/valleys/dormers) require component-by-component takeoffs.