What Is Roof Pitch?
Roof pitch describes the steepness of a roof expressed as a ratio of vertical rise to horizontal run. A pitch of 6/12 means the roof rises 6 inches for every 12 inches of horizontal distance. Pitch affects material choices, load capacity, walkability, and cost.
Method 1: Measure from the Attic (Most Accurate)
This is the most reliable method because you measure directly against the rafters without weather interference.
What You Need
- A 2-foot (24-inch) carpenter's level
- A tape measure
- Access to the attic space
Steps
- Place the level against the underside of a rafter, making sure it's perfectly horizontal (check the bubble).
- Mark 12 inches along the level from the point where it touches the rafter.
- Measure vertically from that 12-inch mark straight down to the rafter surface. This vertical measurement is your rise.
- Record the pitch as rise/12. If you measured 6 inches vertically, your pitch is 6/12.
Pitch = Rise รท Run
Standard format: X/12 (rise per 12 inches of run)
Example: 6" rise over 12" run = 6/12 pitch
Method 2: Speed Square Method
A speed square (rafter square) has a built-in pitch scale along its hypotenuse edge.
- Place the speed square's pivot point on the top edge of a rafter.
- Hang a plumb bob (or hold a level vertical) from the pivot point.
- Read the pitch number where the plumb line crosses the "Common" scale on the hypotenuse. This is your pitch in X/12 format.
Method 3: Measure from the Ground
If you can't access the attic, you can estimate pitch from the ground using a simple photo method.
- Stand far enough from the house to see the entire gable end straight on.
- Take a photo or hold up a ruler at arm's length to measure the visible height of the gable triangle and the visible width of the house at the eave line.
- Calculate: Pitch = (Gable Height ร 24) รท House Width. The result is approximate but useful for estimation.
Pitch-to-Degrees Conversion Table
| Pitch | Degrees | Slope % | Rafter Multiplier |
|---|
| 1/12 | 4.76ยฐ | 8.3% | 1.003 |
| 2/12 | 9.46ยฐ | 16.7% | 1.014 |
| 3/12 | 14.04ยฐ | 25.0% | 1.031 |
| 4/12 | 18.43ยฐ | 33.3% | 1.054 |
| 5/12 | 22.62ยฐ | 41.7% | 1.083 |
| 6/12 | 26.57ยฐ | 50.0% | 1.118 |
| 7/12 | 30.26ยฐ | 58.3% | 1.158 |
| 8/12 | 33.69ยฐ | 66.7% | 1.202 |
| 9/12 | 36.87ยฐ | 75.0% | 1.250 |
| 10/12 | 39.81ยฐ | 83.3% | 1.302 |
| 12/12 | 45.00ยฐ | 100.0% | 1.414 |
Why Pitch Matters
- Material selection: Low-slope roofs (below 3/12) require membrane roofing. Asphalt shingles need at least 2/12.
- Cost: Steeper roofs cost more due to increased safety requirements and labor difficulty. Pitches above 6/12 require roof brackets.
- Snow load: Steeper pitches shed snow faster, reducing structural load in cold climates.
- Roof area: Higher pitch = more roof area for the same footprint, meaning more materials needed.
Calculate Your Roof Pitch Instantly
Use our free calculator to convert between pitch, degrees, and slope percentage โ with an interactive visual diagram.