Roof slope and area planning
Roof Pitch Calculator
Convert roof rise and run into pitch ratio, angle, percent slope, and pitch multiplier. Add building dimensions to estimate roof area, roofing squares, vertical rise, and common-rafter length.
Pitch conversion
Ratio + angle
Roof surface
Area + squares
Rafter planning
Run + length
What this calculator includes
Inputs
Roof pitch details
Enter the vertical rise and horizontal run. Add building dimensions when you also want estimated roof area, roofing squares, and common-rafter length.
Roof-pitch formula
Pitch multiplier = √(rise² + run²) ÷ run. The horizontal roof footprint is multiplied by this factor to estimate the sloped roof surface area.
Results
Roof pitch results
Review the converted pitch, roof slope, area estimate, roofing squares, and common-rafter length.
Roof pitch
6:12
Roof angle
26.57°
Percent slope
50%
Pitch multiplier
1.118
Sloped roof area
1,502.64 sq ft
Roofing squares
15.03
Pitch conversion
Roof dimensions
Rafter estimate
Planning notes
- • The area estimate assumes one rectangular roof footprint with a consistent pitch and overhang.
How to calculate roof pitch
Roof pitch compares vertical rise with horizontal run. A 6:12 pitch rises 6 inches for every 12 inches of horizontal distance. That ratio can be converted into an angle, percent slope, and multiplier using right-triangle calculations.
Step 1
Measure the rise
Measure the vertical change over a known horizontal section of the roof or rafter.
Step 2
Measure the run
Use 12 inches of horizontal run for a standard U.S. pitch ratio, or enter another known run.
Step 3
Review the results
Use the calculated angle, multiplier, area, squares, and rafter length for project planning.
Roof pitch formulas
Roof angle
angle = arctan(rise ÷ run)
The result is converted from radians into degrees.
Percent slope
percent slope = rise ÷ run × 100
A 6:12 pitch produces a 50% slope.
Pitch multiplier
√(rise² + run²) ÷ run
Multiply horizontal roof area by this factor to estimate sloped surface area.
Common-rafter length
horizontal rafter run × pitch multiplier
This is a basic geometric length before ridge, seat-cut, tail, and framing adjustments.
Common roof pitch conversion chart
Use this chart for quick comparisons between common rise-over-12 pitches, roof angles, percent slopes, and pitch multipliers.
| Pitch | Angle | Percent slope | Multiplier |
|---|---|---|---|
| 2:12 | 9.46° | 16.67% | 1.014 |
| 3:12 | 14.04° | 25% | 1.031 |
| 4:12 | 18.43° | 33.33% | 1.054 |
| 5:12 | 22.62° | 41.67% | 1.083 |
| 6:12 | 26.57° | 50% | 1.118 |
| 7:12 | 30.26° | 58.33% | 1.158 |
| 8:12 | 33.69° | 66.67% | 1.202 |
| 9:12 | 36.87° | 75% | 1.250 |
| 10:12 | 39.81° | 83.33% | 1.302 |
| 12:12 | 45° | 100% | 1.414 |
Understanding roof area and roofing squares
A sloped roof has more surface area than its horizontal footprint. The calculator first adds the selected overhang to the building dimensions, then multiplies the horizontal roof area by the pitch multiplier.
One roofing square equals 100 square feet of roof surface. The square result is an area measurement, not a final material order. Shingles, underlayment, starter material, ridge caps, flashing, waste, roof complexity, and product coverage must be calculated separately.
Gable and hip roofs over the same rectangular footprint have approximately the same total geometric surface area when the pitch is consistent. Their material waste and installation requirements can still differ substantially.
Measurement and safety notice
This calculator provides planning estimates for simple roof geometry. It does not replace engineered plans, manufacturer instructions, local building requirements, structural calculations, or field verification. Valleys, hips, dormers, offsets, unequal slopes, ridge details, framing cuts, and complex roof sections can change actual quantities. Avoid climbing or measuring a roof without suitable training, access equipment, and fall protection.
Roof pitch calculator FAQs
How do I calculate roof pitch?
Measure vertical rise over horizontal run. Roof pitch in the United States is commonly written as inches of rise per 12 inches of run, such as 4:12, 6:12, or 8:12.
What angle is a 6:12 roof pitch?
A 6:12 pitch is approximately 26.57 degrees. It also equals a 50% slope and has a pitch multiplier of approximately 1.118.
What does the pitch multiplier calculate?
The multiplier converts a horizontal distance or area into its corresponding sloped measurement. It can be applied to horizontal roof area and horizontal rafter run.
How many square feet are in one roofing square?
One roofing square equals 100 square feet of roof surface. Material orders require product coverage and waste calculations in addition to the geometric roof area.
Is the calculated rafter length a final cut length?
No. It is a basic geometric common-rafter length. Ridge thickness, birdsmouth and seat cuts, tails, overhang framing, lumber dimensions, connections, and construction details may change the final cut length.