Roof Pitch Calculator
Calculate roof pitch, slope percentage and angle.
Project details
Enter your measurements below.
Roof pitch is a geometry description, not a roofing recommendation
Roof work commonly describes slope as rise per 12 units of horizontal run, such as 4:12 or 6:12. The same slope can also be written as an angle or converted to a pitch factor for estimating sloped surface area from plan area. This calculator translates between those forms when the rise and horizontal run are known. It does not determine whether a roof pitch is suitable for a roofing product, climate, drainage condition or structural system. Work at height and roof design require project-specific safety and professional judgment.
Rise-per-12 expresses vertical rise for every 12 units of horizontal run.
The slope factor converts horizontal plan area to approximate sloped roof area.
Geometry only; it does not choose roof pitch or verify structural/product requirements.
How to use the Roof Pitch Calculator
- Measure or obtain the vertical rise and horizontal run for the roof plane.
- Convert the rise/run relationship to a rise-per-12 pitch if that is the convention used by your drawings or roofing product.
- Use arctangent to express the same slope as an angle, or calculate the slope factor for surface-area estimating.
- Verify the resulting pitch against the requirements of the actual roof system before using it for product or construction decisions.
One roof slope, three useful expressions
A 6:12 roof, about 26.6°, and a slope factor of about 1.118 all describe the same basic plane. They are useful for different parts of planning.
Use the pitch in the right tool
Use the factor to estimate sloped area from plan area, and use the rise-per-12 or angle when checking product literature or project documents.
Worked example: a 6:12 roof
- Pitch
- 6:12
- Rise/run
- 6 ÷ 12 = 0.5
- Angle
- ≈ 26.6°
- Slope factor
- ≈ 1.118
A 1,000 sq ft horizontal roof plan would correspond to about 1,118 sq ft of simple sloped plane area before overhangs, valleys, hips or waste are considered.
Practical planning tips
Use horizontal run, not rafter length, when calculating rise-per-12 pitch.
For roofs with several slopes, calculate each plane or pitch family separately.
Do not infer roof accessibility from pitch alone; surface condition, height, weather and fall protection matter.
Check minimum/maximum slope requirements for the exact roofing system rather than assuming a familiar pitch works everywhere.
Common mistakes to avoid
Using the sloped rafter length as the horizontal run.
Treating 6:12 as 6 degrees.
Applying one pitch factor to a roof that contains multiple different slopes.
Using the calculator to choose structural rafters, trusses or roofing-system suitability.
Roof Pitch Calculator FAQs
What does a 6:12 roof pitch mean?+
It means the roof rises 6 units vertically for every 12 units of horizontal run.
Is roof pitch the same as degrees?+
No, but they describe the same slope in different formats. A 6:12 pitch is about 26.6 degrees.
What is a roof slope factor?+
It is the multiplier that converts horizontal plan area to the area of a simple sloped plane.
Does this tell me what pitch my roofing material requires?+
No. Check the manufacturer's installation requirements and project documents for acceptable slopes.