how to figure roof pitch calculator

Quick tip: If your run is exactly 12 inches, then the rise number is already your pitch value (example: rise 7 and run 12 = 7/12 pitch).

What roof pitch means

Roof pitch is a simple way to describe roof steepness. In U.S. construction, pitch is usually written as X in 12. That means the roof rises X units vertically for every 12 units of horizontal run.

• Low pitch: gentler slope, often easier to walk but may need special waterproofing.
• Steeper pitch: sheds water and snow faster, but needs more roofing material and safety care.
• Pitch, slope, and angle all describe steepness, just in different formats.

How this roof slope calculator works

The calculator uses standard geometry formulas. As long as rise and run use the same unit, the results are accurate.

• Slope ratio: rise ÷ run
• Pitch in 12: (rise ÷ run) × 12
• Slope percentage: (rise ÷ run) × 100
• Roof angle: arctan(rise ÷ run)
• Rafter length for measured triangle: √(rise² + run²)

Step-by-step: how to figure roof pitch manually

1) Measure run

Run is the horizontal distance, not along the roof surface. For a simple gable roof, run is usually half the building span from outside wall to ridge centerline.

2) Measure rise

Rise is the vertical gain over that run. If you use a level and tape measure on an existing roof, a common method is measuring rise over a 12-inch run.

3) Convert to pitch

Apply the formula: pitch = (rise / run) × 12. Example: rise 5, run 10 → (5 ÷ 10) × 12 = 6, so the pitch is 6/12.

4) Convert to angle if needed

Some plans, solar designs, and engineering details use degrees. Use arctangent to convert slope ratio into degrees, or use this calculator instantly.

Worked examples

Example A: classic 6/12 roof

If rise is 6 and run is 12:

• Pitch = 6/12
• Angle ≈ 26.57°
• Slope = 50%

Example B: lower slope roof

If rise is 4 and run is 12:

• Pitch = 4/12
• Angle ≈ 18.43°
• Slope = 33.33%

Example C: same pitch, different dimensions

Rise 8 and run 16 gives the same slope ratio as 6 and 12 (both are 1:2), so both represent a 6/12 pitch.

Common roof pitch chart

Pitch	Angle (approx.)	Slope %	Typical use
2/12	9.46°	16.7%	Low-slope sections, porches, modern designs
4/12	18.43°	33.3%	Common residential roofs in mild climates
6/12	26.57°	50.0%	Very common balance of drainage and cost
8/12	33.69°	66.7%	Steeper roofs for snow and traditional styles
10/12	39.81°	83.3%	High visual profile, fast runoff
12/12	45.00°	100%	Very steep architectural roofs

Common mistakes to avoid

• Mixing units (example: rise in inches and run in feet).
• Measuring along the roof instead of horizontal run.
• Using full span when your formula expects half-span (run).
• Ignoring local code and manufacturer minimum pitch requirements.

FAQ

Is roof pitch the same as roof angle?

Not exactly. Pitch is usually written as rise over 12, while angle is measured in degrees. They represent the same geometry in different formats.

What pitch is walkable?

That depends on safety setup, footwear, weather, and training. Even lower pitches can be dangerous when wet or dusty. Use proper fall protection.

Can I calculate materials from pitch alone?

Pitch helps, but you still need roof dimensions, overhangs, valleys, waste factors, and product-specific coverage rates for accurate material estimates.

Bottom line

If you know rise and run, you can quickly determine roof pitch, slope percentage, angle, and rafter geometry. Use the calculator above for fast results, then verify critical numbers against building plans and local code requirements before purchasing materials or starting work.