Use this roof pitch calculator to convert rise and run into an x:12 pitch, roof angle, slope percentage and pitch factor. Add simple gable-roof dimensions to estimate ridge rise, sloped rafter distance and surface area before checking plans with a qualified roofing or building professional.
Calculate Roof Pitch, Rafter Length and Roof Area
Choose how the pitch is known, then enter the simple gable-roof dimensions in feet or metres.
What Is Roof Pitch?
Roof pitch describes how much a roof rises vertically for a given horizontal run. In the United States, it is commonly written as rise over 12 units of run. A 6:12 pitch rises 6 inches for every 12 inches of horizontal travel. Because the relationship is a ratio, the same geometry also rises 6 centimetres for every 12 centimetres.
Pitch, angle and slope percentage describe the same incline in different formats. They should not be confused with the total roof height, rafter size or structural capacity. Those depend on building dimensions, framing details, loads, material and local requirements.
Roof Pitch Formulas
Let p be the rise per 12 units of run. The calculator uses trigonometry and the Pythagorean theorem to convert between roof measurements.
Pitch ratio = rise / run x 12
Angle = arctan(p / 12)
Slope percentage = (p / 12) x 100
Pitch factor = square root of [1 + (p / 12)2]
Rafter line = horizontal roof run x pitch factor
For the simple symmetrical gable model used here, horizontal roof run equals half the building width plus the eave overhang. The area equals two roof planes multiplied by the sloped rafter line and roof length, including the entered gable-end overhang.
Roof Pitch Conversion Chart
This chart converts common x:12 roof pitches to approximate angles, slope percentages and pitch factors. The pitch factor converts horizontal run to sloped roof distance.
| Pitch | Angle | Slope | Pitch factor | Sloped distance per 12 run |
|---|---|---|---|---|
| 2:12 | 9.46 degrees | 16.67% | 1.014 | 12.17 units |
| 3:12 | 14.04 degrees | 25% | 1.031 | 12.37 units |
| 4:12 | 18.43 degrees | 33.33% | 1.054 | 12.65 units |
| 5:12 | 22.62 degrees | 41.67% | 1.083 | 13.00 units |
| 6:12 | 26.57 degrees | 50% | 1.118 | 13.42 units |
| 8:12 | 33.69 degrees | 66.67% | 1.202 | 14.42 units |
| 10:12 | 39.81 degrees | 83.33% | 1.302 | 15.62 units |
| 12:12 | 45 degrees | 100% | 1.414 | 16.97 units |
How to Measure Roof Pitch Safely
The safest measurement often comes from approved plans, framing drawings or an accessible attic rather than walking on the roof. In an attic, hold a level horizontally against a rafter, mark a 12-inch run and measure vertically from the level to the underside of the rafter. That vertical distance is the approximate rise per 12.
- Confirm that the horizontal reference is level.
- Measure exactly 12 units along that horizontal reference.
- Measure the vertical rise to the roof plane at the 12-unit mark.
- Repeat in another location and compare the readings.
- Use construction documents or a professional survey when accuracy affects ordering or structural work.
Fall-safety notice: Roofs and ladders create serious fall hazards. OSHA identifies falls as a leading cause of death in residential construction and requires fall protection for covered roofing work. Do not climb onto a roof solely to use this calculator; use plans, an accessible interior measurement or a qualified professional.
Roofing Material and Minimum-Slope Considerations
A geometric calculation does not decide whether a roofing product is permitted. The adopted building code, roof assembly, climate, drainage design and manufacturer's installation instructions control. The 2024 International Residential Code states that asphalt shingles are used only on slopes of 2:12 or greater. Slopes from 2:12 to less than 4:12 need the applicable low-slope underlayment provisions.
GAF similarly describes 2:12 as the general absolute minimum for shingles and identifies 2:12 up to, but not including, 4:12 as a low-slope shingle range requiring additional deck protection. Product-specific instructions can be more restrictive. Metal panels, membranes, tiles, slate and other systems have different limits and details.
- Check the code edition adopted by the local authority.
- Read the exact product's current installation instructions.
- Confirm underlayment, flashing, ventilation and fastener requirements.
- Have drainage and structural loads reviewed for the actual building.
Worked Roof Pitch Example
Consider a 30-foot-wide, 40-foot-long simple gable building with a 6:12 pitch, 1-foot eave overhangs, 1-foot gable overhangs and a 10% planning allowance.
This is a geometric surface estimate, not a material order. Valleys, hips, dormers, openings, starter courses, laps, bundle coverage and product layout can materially change the quantity.
What the Roof Area Estimate Includes
The area portion is designed for a symmetrical two-plane gable roof. It includes the entered eave and gable overhangs, then adds the chosen planning allowance. It does not model complex intersections or structural framing.
Included in the estimate
- Two equal rectangular roof planes
- One continuous ridge
- Equal eave overhangs on both sides
- Equal gable overhangs at both ends
Not included
- Hip and valley geometry, dormers, crickets or multiple roof levels
- Rafter birdsmouths, ridge-board deductions, fascia details or cut lengths
- Structural member sizing, snow loads, wind loads or deflection checks
- Product coverage, laps, starter strips, cap material or local waste patterns
Related Home and Property Calculators
Roof geometry is only one part of a property project. Compare broader property estimates with the property valuation calculator, review financing with the mortgage calculator, browse country-specific tools in the Global Calculators directory, or explore more free financial calculators and money tools from 1Dollars.
Roof Pitch Calculator FAQs
How do I calculate roof pitch?
Divide vertical rise by horizontal run and multiply by 12. A roof that rises 6 units over a 12-unit run has a 6:12 pitch.
What angle is a 6:12 roof pitch?
A 6:12 pitch is approximately 26.57 degrees because arctan(6 / 12) equals about 26.57 degrees.
What roof pitch is 30 degrees?
A 30-degree roof has a rise per 12 of about 6.93, so it is approximately a 6.93:12 pitch.
How do I convert roof pitch to slope percentage?
Divide the rise number by 12 and multiply by 100. For example, 6 / 12 x 100 equals a 50% slope.
What is the roof pitch factor?
The pitch factor converts horizontal run into sloped roof distance. It equals the square root of 1 plus the square of rise divided by run. A 6:12 pitch factor is about 1.118.
How does the calculator estimate rafter length?
It multiplies half the building width plus the eave overhang by the pitch factor. This is a geometric slope line, not a final rafter cut length or structural design.
How does the calculator estimate roof area?
For a simple gable roof, it multiplies the rafter line by the roof length including gable overhangs, then doubles the result for two equal roof planes.
Is 2:12 the minimum pitch for asphalt shingles?
The 2024 IRC sets 2:12 as the minimum slope for asphalt shingles and applies additional provisions below 4:12. Always follow the locally adopted code and the exact manufacturer's instructions.
Can I use this calculator for a hip roof?
The pitch conversions still apply, but the area model assumes two rectangular gable planes. A hip roof needs separate geometry for its sloped triangular or trapezoidal planes.
Does this calculator size rafters or determine roof loads?
No. It does not calculate member size, span capacity, connections, wind, snow, seismic or dead loads. A qualified designer must evaluate the actual structure and local requirements.
Methodology, Sources and Safety
The calculator applies standard right-triangle geometry to user-entered measurements. Results are rounded for display while calculations retain additional precision in the browser. The roof-area estimate is limited to the simple gable assumptions stated above.
- 2024 International Residential Code, Section R905.2.2: Asphalt-shingle slope
- GAF: Minimum Slope for Shingles
- OSHA: Fall Protection in Residential Construction
- OSHA: Protecting Roofing Workers
Editorial review and last fact-check: July 19, 2026.
Disclaimer: This calculator provides preliminary geometric estimates for educational planning. It is not architectural, engineering, code, roofing, safety or procurement advice. Do not use it to size structural members, determine loads, select an approved roof system or replace field measurements and current product instructions. Codes and manufacturer requirements vary and can change. Use qualified professionals for design, measurement, installation and work at height.