Determine the slope, angle, and pitch ratio of your roof.
Please enter valid positive numbers for both Rise and Run.
Pitch Ratio:0 / 12
Angle (Degrees):0°
Grade (Percentage):0%
Slope Factor:1.0
function calculateRoofPitch() {
var rise = parseFloat(document.getElementById('roofRise').value);
var run = parseFloat(document.getElementById('roofRun').value);
var errorDiv = document.getElementById('roofError');
var resultsDiv = document.getElementById('roofResults');
if (isNaN(rise) || isNaN(run) || run <= 0 || rise < 0) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
// Calculate pitch based on a standard 12-inch run
var pitchValue = (rise / run) * 12;
var angleRad = Math.atan(rise / run);
var angleDeg = angleRad * (180 / Math.PI);
var percentage = (rise / run) * 100;
// Slope factor (multiplier for rafter length)
var slopeFactor = Math.sqrt(Math.pow(rise, 2) + Math.pow(run, 2)) / run;
document.getElementById('resPitch').innerText = pitchValue.toFixed(2) + " / 12";
document.getElementById('resAngle').innerText = angleDeg.toFixed(2) + "°";
document.getElementById('resGrade').innerText = percentage.toFixed(2) + "%";
document.getElementById('resFactor').innerText = slopeFactor.toFixed(3);
resultsDiv.style.display = 'block';
}
Understanding Roof Pitch: A Complete Guide
Roof pitch is a critical measurement in construction and roofing that describes the steepness of a roof. It is expressed as a ratio of the vertical "rise" to the horizontal "run." For example, a "6/12" pitch means the roof rises 6 inches for every 12 inches it extends horizontally.
The Components of Roof Pitch
Rise: The vertical height measured from the top of the wall plate to the ridge of the roof.
Run: The horizontal distance from the outside of the wall to a point directly below the ridge (usually half the span of the building).
Pitch Ratio: Traditionally expressed in inches of rise per 12 inches of run.
How to Figure Roof Pitch Manually
To calculate your roof pitch manually, you need a level and a tape measure. Place one end of the level against the roof surface, hold it perfectly level, and measure 12 inches out. From that 12-inch mark, measure the vertical distance down to the roof. This vertical measurement is your rise over a 12-inch run.
Formula:(Rise / Run) x 12 = Pitch
Common Roof Pitch Examples
Pitch (x/12)
Angle (Degrees)
Description
1/12 – 3/12
4.76° – 14.04°
Low Slope (Requires special roofing)
4/12 – 9/12
18.43° – 36.87°
Conventional Slope
10/12 – 12/12
39.81° – 45.00°
Steep Slope
Why Does Pitch Matter?
Pitch dictates what kind of materials you can use on your roof. Standard asphalt shingles generally require at least a 2/12 pitch with specialized underlayment, or 4/12 for standard installation. Steep roofs shed water and snow more efficiently but are more difficult and dangerous for contractors to walk on, often leading to higher labor costs.
What is a Slope Factor?
The Slope Factor (or Pitch Multiplier) is a number used to calculate the actual length of the rafters or the total surface area of a roof based on the flat footprint. By multiplying the horizontal area by the slope factor, you can determine exactly how much material (like shingles or plywood) you need to purchase for the project.