How to Measure Roof Pitch
A step-by-step contractor guide to measuring roof slope accurately using safe interior attic methods, architectural elevation plans, and ground-based geometry.
Walking across a pitched roof introduces severe fall hazards. Professional estimators prioritize safe, non-invasive measurement methods from an accessible interior attic, architectural blueprints, or ground-level elevation geometry whenever possible. Never climb onto a steep or wet roof without proper OSHA-compliant fall arrest equipment.
Method 1: Measuring from the Attic (Safest & Most Accurate)
Measuring the underside of an exposed common rafter inside your attic provides the highest precision because the structural lumber has a uniform, laser-straight edge unaffected by shingle grit, curling layers, or gutters.
Place one end of a 12-inch carpenter's level flush against the bottom edge of a straight roof rafter.
Pivot the loose end of the level until the center spirit vial bubble is perfectly centered between the indicator lines.
From the 12-inch mark on your level, use a tape measure to measure vertically straight up to the underside of the rafter.
If the tape reads 5 inches, your roof has a 5/12 pitch (5 inches of vertical rise per 12 inches of horizontal run).
Method 2: Calculating Pitch from Blueprints or Total Dimensions
If you have building plans or can measure exterior wall dimensions, calculate pitch mathematically from the total roof rise and building span:
Example: A detached garage measures 24 feet wide (half-span = 12 ft). The ridge board stands 6 feet higher than the exterior wall plates. Pitch = (6 ÷ 12) × 12 = 6/12 pitch.
Method 3: Ground-Based Inclinometer & Optical Methods
For houses with finished attics and no blueprints, step back across your yard until you can view the gable rake edge perpendicularly. Using a smartphone pitch gauge app or digital angle finder, align the tool edge with the rake angle. Use our roof pitch chart to match the measured degree angle to the nearest standard pitch.
Converting Your Measurement to Other Roofing Units
Once you have determined your rise over 12 inches of run, convert it to any other standard construction metric:
arctan(Rise ÷ 12) × (180 ÷ π)(Rise ÷ 12) × 100√(1 + (Rise ÷ 12)²)Frequently Asked Questions
What is the safest way to measure roof pitch?
The safest and most accurate way to measure roof pitch is from the interior of an accessible attic. Placing a 12-inch level against the underside of an exposed roof rafter eliminates fall hazards and prevents measurement distortion caused by uneven or damaged exterior shingles.
What tools do I need to measure roof pitch in an attic?
You only need two basic tools: a standard 12-inch carpenter's torpedo level (or 24-inch level) and a standard tape measure. Hold the level horizontal against the underside of a rafter, center the bubble, and measure vertically from the 12-inch mark on the level to the bottom edge of the rafter.
Can I measure roof pitch from the ground?
Yes. You can estimate pitch from the ground by stepping back to view the gable end of the house perpendicularly. You can use a digital inclinometer smartphone app (such as a pitch gauge app) aligned with the roof rake line, or calculate the rise from the height difference between the eave line and ridge line divided by half the building width.
How do I calculate pitch if I use a 24-inch level?
If using a 24-inch level, hold it horizontal, measure the vertical rise at the 24-inch mark, and divide that measurement by 2 to find the standard rise over a 12-inch run. For example, if you measure 10 inches of rise at the 24-inch mark: 10 ÷ 2 = 5 inches of rise per 12 inches of run (a 5:12 pitch).
How do I convert my measured pitch into an angle in degrees?
Divide your measured rise by 12, then calculate the arctangent of that number: Angle = arctan(Rise / 12) × (180 / π). For example, a 6-inch rise over 12 inches yields: arctan(6 / 12) = arctan(0.5) ≈ 26.57 degrees. Use our interactive [Roof Pitch Calculator](/roof-pitch-calculator/) for instant conversion.