Determine the slope, angle, and ratio of your roof.
Calculated Results:
Pitch Ratio:
Angle (Degrees): °
Slope Percentage: %
Roof Classification:
How Do You Calculate the Pitch of a Roof?
Understanding roof pitch is essential for roofing contractors, architects, and DIY homeowners alike. Roof pitch refers to the steepness of a roof, and it is traditionally expressed as a ratio of the vertical "rise" over the horizontal "run."
The Basic Pitch Formula
In the United States, roof pitch is most commonly measured by how many inches the roof rises vertically for every 12 inches it extends horizontally. The formula is expressed as:
Pitch = Rise / Run
For example, if a roof rises 6 inches for every 12 inches of horizontal distance, it is known as a "6:12 pitch."
Steps to Measure Roof Pitch Manually
Access the Attic or Roof: You can measure from the rafters inside an unfinished attic or directly on the roof surface.
Set the Level: Use a 12-inch level (or mark 12 inches on a longer level). Hold it perfectly horizontal.
Measure the Vertical Distance: From the 12-inch mark on your level, measure the vertical distance down to the roof surface or rafter.
Record the Measurement: This vertical number is your "Rise." Since your level represents 12 inches of "Run," your pitch is simply [Rise]:12.
Calculating the Angle in Degrees
If you prefer to know the angle in degrees rather than a ratio, you can use trigonometry. The angle of a roof is the arctan(Rise / Run). Converting this to degrees provides the exact slope angle used in many architectural drawings.
Common Roof Classifications
Flat Roofs: 0:12 to 2:12 pitch (actually slightly sloped for drainage).
Low Slope: 2:12 to 4:12 pitch.
Conventional Slope: 4:12 to 9:12 pitch.
Steep Slope: 9:12 and higher (often seen in Victorian or Gothic styles).
Why Roof Pitch Matters
The pitch of your roof determines which roofing materials can be safely installed. For instance, standard asphalt shingles are generally not recommended for pitches below 2:12 because water can easily seep under the shingles. Steeper roofs shed water and snow more effectively but are more dangerous and expensive to work on due to the increased surface area and safety equipment required.
function calculatePitch() {
var rise = parseFloat(document.getElementById('roofRise').value);
var run = parseFloat(document.getElementById('roofRun').value);
var resultDiv = document.getElementById('roofResult');
if (isNaN(rise) || isNaN(run) || run <= 0 || rise < 0) {
alert("Please enter valid positive numbers for Rise and Run.");
return;
}
// 1. Calculate Ratio based on 12-inch standard
var normalizedRise = (rise / run) * 12;
var ratioString = normalizedRise.toFixed(2).replace(/\.00$/, '') + " : 12";
// 2. Calculate Angle (Degrees)
var radians = Math.atan(rise / run);
var degrees = radians * (180 / Math.PI);
// 3. Calculate Slope Percentage
var percentage = (rise / run) * 100;
// 4. Determine Roof Type
var type = "";
if (normalizedRise < 2) {
type = "Flat / Very Low Slope";
} else if (normalizedRise < 4) {
type = "Low Slope";
} else if (normalizedRise < 9) {
type = "Conventional Slope";
} else {
type = "Steep Slope";
}
// Display results
document.getElementById('pitchRatio').innerHTML = ratioString;
document.getElementById('pitchAngle').innerHTML = degrees.toFixed(2);
document.getElementById('pitchPercent').innerHTML = percentage.toFixed(2);
document.getElementById('roofType').innerHTML = type;
resultDiv.style.display = 'block';
}