Roof Pitch Calculator — Find Your Roof Slope & Pitch Multiplier
Calculate your roof pitch as an X/12 ratio, angle in degrees, and pitch multiplier. Enter rise and run, or convert from a known angle or percentage.
How to Use This Calculator
- Select how you want to enter your pitch information
- Enter rise (vertical) and run (horizontal, typically 12") measurements
- Or enter a known angle in degrees, or the rise portion of a X/12 pitch
- Click "Calculate Roof Pitch" to see all pitch measurements and the multiplier
How the Calculation Works
pitch_ratio = rise / run // expressed as rise:12 (e.g., 4:12)
angle_degrees = atan(rise / run) × (180 / π)
pitch_multiplier = sqrt(1 + (rise / run)²)
pitch_percentage = (rise / run) × 100 Roof pitch is expressed as rise per 12 inches of horizontal run. The angle in degrees uses the arctangent of rise/run. The pitch multiplier is the key value for material calculations — multiply your horizontal footprint area by the multiplier to get actual roof surface area. For example, a 6/12 pitch has a multiplier of 1.118, meaning 1000 sqft footprint = 1118 sqft of actual roof area.
Variables:
- pitch_ratio: Rise per 12 inches of run (standard notation e.g., 4/12)
- angle_degrees: Equivalent angle of the roof slope in degrees
- pitch_multiplier: Factor to multiply footprint area to get actual roof area
- pitch_percentage: Slope expressed as a percentage (rise ÷ run × 100)
Pro Tips
- Always use proper fall protection (harness and anchor) on roofs with a pitch steeper than 6/12
- The pitch multiplier converts horizontal footprint area to actual roof surface area
- A 4/12 pitch is the most common residential pitch — good balance of water shedding and walkability
- Roofs below 2/12 require special low-slope roofing materials (rolled roofing, membrane)
- Measure rise and run from the attic: hold a level 12" horizontally from the rafter and measure up to the rafter surface
Recommended Products
Frequently Asked Questions
What is a common roof pitch?
4/12 is the most common residential pitch — it sheds water well and is still walkable. 6/12 provides good drainage and curb appeal. Pitches below 3/12 require special low-slope materials; pitches above 9/12 are steep and require safety equipment.
How do I measure my roof pitch from the ground?
You can estimate pitch from gable end geometry using a protractor app on your phone, or from the attic using a 12" level and tape measure. Hold the level horizontal against the rafter and measure the vertical distance to the rafter at the 12" mark — that measurement is your rise.
What does pitch multiplier mean?
The pitch multiplier converts your roof's horizontal footprint to actual sloped surface area. A flat roof has a multiplier of 1.0. A 4/12 pitch has 1.054, meaning a 1000 sqft footprint is actually 1054 sqft of roof surface to cover with materials.
What roofing materials work on low-pitch roofs?
Below 2/12: TPO, EPDM rubber membrane, or built-up roofing only. 2/12 to 4/12: rolled roofing or special low-slope shingles with extra underlayment. Above 4/12: all standard roofing materials including asphalt shingles, metal, tile, and wood shakes.
Is a 4/12 roof walkable?
A 4/12 pitch is considered walkable by most professional roofers without special equipment, though grip soles are still recommended. Above 7/12, roof brackets or jacks are strongly recommended. Above 9/12, a safety harness is required.