How to Measure Roof Pitch: Inside & Outside Methods
Roof pitch is the slope expressed as rise over run (e.g., 6/12 means 6 inches of rise per 12 inches of horizontal distance). Knowing your pitch is essential for calculating roof area, ordering materials, and choosing the right roofing products.
What You Will Need
- A 24-inch or 48-inch level
- A tape measure
- A pencil and paper (or your phone)
- Optional: a pitch finder / angle gauge tool ($10-$20)
Method 1: From Inside the Attic (Safest)
The safest method — stay inside the building. Works on any roof where you can access the underside of the rafters.
Access the attic
Go into the attic and find an exposed rafter.
Place the level
Hold the level horizontally against the bottom edge of a rafter. Make sure the bubble is centered (perfectly level).
Mark 12 inches
From the point where the level touches the rafter, measure 12 inches along the level and make a mark.
Measure the rise
From your 12-inch mark, measure vertically down to the rafter. This measurement is the rise.
Read the pitch
If you measured 6 inches of rise over 12 inches of run, your pitch is 6/12.
For a more detailed walkthrough, see our guide to determining pitch from inside the attic.
Method 2: From Outside on the Roof
Safety Warning
Use a stable ladder and safety harness. Never work on a wet or icy roof.
Climb safely
Use a stable ladder and safety harness. Never work on a wet or icy roof.
Place the level on the roof surface
Set one end of the level at the roofline and hold it perfectly horizontal.
Mark 12 inches
Measure 12 inches from the low end of the level along the level itself.
Measure down to the roof
From the 12-inch mark, measure vertically down to the roof surface.
Read the pitch
That vertical measurement is your rise per 12 inches of run.
Method 3: Smartphone Apps
Pro Tip
Several smartphone apps use the phone's built-in inclinometer to measure roof pitch. Hold the phone against a rafter in the attic or along the roof surface. While convenient, these apps are typically accurate to within 1-2 degrees (about half a pitch increment). Use them for rough estimates and verify with the level method for material ordering.
Common Roof Pitches and What They Mean
| Pitch | Degrees | Category | Notes |
|---|---|---|---|
| 1/12 - 2/12 | 4.8 - 9.5 | Low slope | Requires special materials (TPO, EPDM, built-up) |
| 3/12 - 4/12 | 14 - 18.4 | Moderate | Minimum for asphalt shingles |
| 5/12 - 8/12 | 22.6 - 33.7 | Standard | Most common residential pitch range |
| 9/12 - 12/12 | 36.9 - 45 | Steep | Requires extra fasteners, safety equipment |
| 12/12+ | 45+ | Very steep | Specialty installation required |
Using Your Pitch Measurement
Calculate roof area
Multiply your footprint by the pitch multiplier.
Calculate rafter length
See our rafter length guide.
Determine material requirements
Use the Roof Pitch Calculator for automatic conversions.
Assess walkability
Under 6/12 is walkable for most people. 6/12-8/12 requires caution. Over 8/12 requires safety equipment.