Knowing how to work out roof pitch helps with roof repairs, material estimates, drainage checks, solar planning, and home projects. Roof pitch describes how steep a roof is, usually as inches of vertical rise for every 12 inches of horizontal run. A pitch such as 6:12 means the roof rises 6 inches for each 12 inches horizontally. The measurement can be calculated from a roof, attic, or building plan, but the safest approach is to measure from a stable location rather than climbing onto a roof.
What Roof Pitch Means
Roof pitch is the slope of a roof, expressed as a ratio of vertical rise to horizontal run. In the common U.S. format, the run is standardized at 12 inches. A 4:12 pitch, for example, rises 4 inches over a 12-inch horizontal distance. A 9:12 pitch rises 9 inches over the same distance.
Pitch is not the same as the roof’s angle in degrees. It is also not the same as the length of a rafter or the distance measured along the roof surface. The distinction matters: a 6:12 pitch has a 6-inch rise per 12 inches of horizontal run, even though the distance along the sloping roof is longer than 12 inches.
Roof pitch is commonly described as low-slope, conventional, or steep-slope, but boundaries vary by building code, roofing material, and industry convention. For example, some roofing products have specific minimum-slope requirements. Those requirements should be checked in the manufacturer’s installation instructions and applicable local building codes—not inferred from a general pitch label.
Roof Pitch Formula
The basic formula is:
Roof pitch = (vertical rise ÷ horizontal run) × 12
Measure rise and run in the same units. The result is the number of inches the roof rises for every 12 inches of horizontal run. For instance, if a roof rises 5 inches over a 12-inch run, its pitch is 5:12. If the measured rise is 10 inches over a 24-inch run, the calculation is (10 ÷ 24) × 12 = 5, so the pitch is also 5:12.
The ratio can also be written as a fraction, such as 5/12, or as a decimal slope. A 5:12 pitch has a decimal slope of 5 ÷ 12, or about 0.417. To express that slope as a percentage, multiply by 100: approximately 41.7%. The percentage describes vertical change relative to horizontal distance; it does not mean the roof angle is 41.7 degrees.
How to Work Out Roof Pitch With a Level and Tape Measure
A level and tape measure can provide a reliable measurement from an accessible roof edge, exposed rafter, or other suitable location. A 12-inch level makes the calculation especially simple. The method measures a horizontal run and the vertical rise at its end.
- Choose a safe measuring point. Prefer an accessible eave or exposed framing. Do not step onto a roof unless the work can be done safely with appropriate equipment and experience.
- Hold the level horizontally. Place one end at the roof surface or rafter and extend the level inward. Adjust it until the bubble indicates level.
- Measure the run. Use 12 inches of horizontal level length if possible. If the level is shorter or longer, record its actual horizontal length.
- Measure the rise. At the far end of the level, measure vertically from the level’s bottom edge to the roof surface or rafter.
- Calculate the pitch. Divide the vertical rise by the horizontal run and multiply by 12.
Example: If the roof surface is 7 inches above the level at the end of a 12-inch horizontal run, the roof pitch is 7:12. If the run is 16 inches and the rise is 8 inches, the pitch is (8 ÷ 16) × 12 = 6:12.
For accurate results, keep the level truly horizontal and the rise measurement vertical. A level that tilts or a tape measure placed along the roof slope can distort the result. Measuring more than once, and at more than one location when appropriate, can reveal measurement errors or roof sections with different slopes.
How to Calculate Pitch From Roof Measurements
Sometimes the required measurements are already available from a plan, framing diagram, or accessible attic. The same formula applies: divide the vertical rise by the horizontal run, then multiply by 12. The key is to identify the correct reference points and distinguish horizontal distance from the sloped rafter length.
Using the ridge and wall plate
For a simple gable roof, the rise is the vertical distance from the top of the exterior wall or wall plate to the roof ridge. The run is the horizontal distance from the outside wall to the roof’s centerline. On a symmetrical gable roof, that run is generally half the building’s span, measured between the relevant exterior wall reference points.
For example, suppose a gable roof spans 28 feet from one exterior wall to the other, and the ridge is 7 feet above the wall plate. The half-span is 14 feet. The pitch is (7 ÷ 14) × 12 = 6, or 6:12. This approach assumes the roof is symmetrical and that the rise and span use matching reference points. Complex framing, overhangs, and unequal roof slopes may require a more careful measurement.
Using an attic rafter
If a rafter is exposed, measure its horizontal run and vertical rise rather than treating the rafter’s sloped length as the run. A framing square or a level and tape can help establish those dimensions. The rafter length alone is not enough to determine pitch unless another dimension is known, because different combinations of rise and run can produce different roof slopes.
Convert Roof Pitch to Degrees
Roof pitch can be converted to an angle using the arctangent function:
Roof angle in degrees = arctan(rise ÷ run)
For a 6:12 roof, the rise-to-run ratio is 6 ÷ 12 = 0.5. The arctangent of 0.5 is approximately 26.6 degrees. A calculator with a trigonometric function, a roof-pitch app, or an online calculator can perform the conversion. The calculator must be set to degrees when displaying the answer in degrees.
For a pitch stated as inches per 12 inches, the formula can be written as angle = arctan(pitch ÷ 12). The reverse conversion is pitch per 12 = 12 × tan(angle). Angle measurements are useful for some tools and design calculations, but U.S. roofing estimates and building plans often use the rise-per-12 convention.
Common Roof Pitch Conversions
| Pitch | Rise per 12 inches | Approximate angle | Approximate slope |
|---|---|---|---|
| 2:12 | 2 inches | 9.5° | 16.7% |
| 3:12 | 3 inches | 14.0° | 25.0% |
| 4:12 | 4 inches | 18.4° | 33.3% |
| 5:12 | 5 inches | 22.6° | 41.7% |
| 6:12 | 6 inches | 26.6° | 50.0% |
| 8:12 | 8 inches | 33.7° | 66.7% |
| 10:12 | 10 inches | 39.8° | 83.3% |
| 12:12 | 12 inches | 45.0° | 100.0% |
Values are rounded. The angle and percentage are mathematical conversions of the pitch, not separate ways to label a roof in the standard rise-per-12 format.
Find Roof Pitch With an Angle Finder or Smartphone
An angle finder can measure a roof surface or rafter directly, if it can be placed securely and aligned with the slope. Once the angle is known, use the conversion formula to find pitch: 12 × tan(angle). For example, a measured angle of about 30 degrees gives a pitch of 12 × tan(30°), or approximately 6.9:12—typically rounded to about 7:12 for a practical description.
Some digital levels and smartphone apps display slope as degrees, percent, or rise per 12 inches. Check which unit the tool is showing before recording the answer. Smartphone sensors may be affected by calibration, case shape, or an uneven surface. For a measurement that will guide construction or material ordering, verify it with a level and tape measure or another suitable instrument.
How Roof Pitch Affects Materials and Planning
Pitch influences how rain and snow move across a roof, the appearance of the roofline, and which roofing products can be installed. It also affects the amount of roofing surface compared with the building’s horizontal footprint. A steeper roof generally has more surface area than a lower-pitch roof covering the same footprint, which can affect material quantities and installation planning.
Pitch alone does not determine whether a roof is suitable for a specific climate or covering. Drainage also depends on roof design, valleys, gutters, penetrations, flashing, and installation quality. Snow loads, wind exposure, and local code requirements involve additional design factors. Product manufacturers specify acceptable slopes and installation details for their systems, so those instructions should be consulted before choosing materials.
For a rough area estimate on a simple, symmetrical gable roof, the sloped length from the eave to the ridge can be found using the Pythagorean theorem: sloped length = √(run² + rise²). Multiply that sloped length by the roof’s length to estimate one roof plane, then account for the second plane and any overhangs. Actual roofing estimates must also consider hips, valleys, dormers, waste, and other details.
Common Roof Pitch Measurement Mistakes
- Using the sloped distance as the run: The run is horizontal, not the length measured along a rafter or roof surface.
- Mixing units: Convert measurements to the same unit before dividing. A rise in inches and run in feet cannot be used directly without conversion.
- Confusing pitch with degrees: A 6:12 pitch is approximately 26.6 degrees, not 6 degrees or 12 degrees.
- Measuring from inconsistent points: The rise and run must refer to the same roof section and compatible framing references.
- Assuming every roof plane matches: Dormers, additions, shed roofs, and architectural features can have different pitches on the same house.
- Rounding too early: Keep the original measurements through the calculation, then round the final pitch to a practical level.
Roof Measurement Safety
Roof work involves fall hazards, and a pitch measurement rarely requires walking on the roof. Safer options include measuring an exposed rafter from inside an attic, using an accessible eave, reviewing construction plans, or hiring a qualified roofing professional. A ladder should be placed on firm, level ground and used according to its instructions. Wet, icy, windy, or damaged roofs should not be approached for a casual measurement.
The U.S. Occupational Safety and Health Administration (OSHA) provides construction fall-protection requirements and safety guidance, including provisions for work on roofs. Requirements depend on the work, site, and applicable regulations. OSHA information is available at osha.gov/fall-protection. For an estimate, inspection, or repair involving roof access, a qualified professional can assess both the pitch and the hazards.
Quick Roof Pitch Reference
To work out roof pitch, measure the roof’s vertical rise over a known horizontal run. Divide rise by run and multiply by 12. A 5-inch rise over 12 inches of run is 5:12; a 10-inch rise over 24 inches is also 5:12. If the measurement is an angle, calculate 12 × tan(angle) to convert it to rise per 12 inches. Keep the measurement method consistent, check the units, and use manufacturer guidance and local requirements when the result will affect roofing materials or construction.