Monthly Interest Rate Calculator Formula

Roof Pitch & Angle Calculator

Enter the vertical rise and horizontal run measurements to calculate your roof's pitch ratio, steepness in degrees, and approximate rafter length.

Ensure Rise and Run use the same unit of measurement.

function calculateRoofPitch() { // Get input values var riseInput = document.getElementById('roofRise').value; var runInput = document.getElementById('roofRun').value; var resultDiv = document.getElementById('pitchResult'); // Validate inputs if (riseInput === "" || runInput === "" || isNaN(riseInput) || isNaN(runInput)) { resultDiv.style.display = "block"; resultDiv.innerHTML = "Please enter valid numbers for both Rise and Run."; return; } var rise = parseFloat(riseInput); var run = parseFloat(runInput); if (run <= 0) { resultDiv.style.display = "block"; resultDiv.innerHTML = "Horizontal Run must be greater than zero."; return; } if (rise < 0) { resultDiv.style.display = "block"; resultDiv.innerHTML = "Vertical Rise cannot be negative."; return; } // Calculate Standard Pitch Ratio (X/12) // Formula: (Rise / Run) * 12 var pitchRatioVal = (rise / run) * 12; var pitchRatioFormatted = pitchRatioVal.toFixed(1) + "/12"; // Calculate Angle in Degrees // Formula: arctan(Rise / Run) * (180 / PI) var radians = Math.atan(rise / run); var degrees = radians * (180 / Math.PI); var degreesFormatted = degrees.toFixed(1) + "°"; // Calculate Rafter Length (Hypotenuse) // Formula: sqrt(Rise^2 + Run^2) var rafterLength = Math.sqrt(Math.pow(rise, 2) + Math.pow(run, 2)); var rafterLengthFormatted = rafterLength.toFixed(2); // Determine Slope Category var slopeCategory = ""; if (pitchRatioVal <= 2) { slopeCategory = "Low Slope (Flat Roof territory)"; } else if (pitchRatioVal <= 4) { slopeCategory = "Low Slope"; } else if (pitchRatioVal <= 9) { slopeCategory = "Medium Slope (Conventional)"; } else { slopeCategory = "Steep Slope"; } // Display results resultDiv.style.display = "block"; resultDiv.innerHTML = `

Calculation Results:

Standard Pitch: ${pitchRatioFormatted} Angle: ${degreesFormatted} Slope Category: ${slopeCategory} Approx. Rafter Length: ${rafterLengthFormatted} (same units as input) Rafter length does not include overhangs. `; }

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Understanding Roof Pitch and Why It Matters

Roof pitch is a critical measurement in construction and roofing that describes the steepness or slope of a roof. It determines not only the aesthetic look of a building but also what types of roofing materials can be used and how effectively the roof sheds water, snow, and debris.

Pitch is most commonly expressed as a ratio representing the vertical rise over a specific horizontal run. In the United States, the standard convention is to measure the rise in inches for every 12 inches (1 foot) of horizontal run.

How to Read Roof Pitch

If you see a roof described as having a "6/12 pitch," it means that for every 12 horizontal inches you travel across the roof, the height rises by 6 inches.

• Low slope roofs (e.g., 2/12 to 4/12) are common on modern homes or commercial buildings but require specific waterproof membrane materials because water drains slowly.
• Medium slope roofs (e.g., 4/12 to 9/12) are the most common for residential housing, allowing for standard asphalt shingles.
• Steep slope roofs (e.g., 10/12 and above) shed water and snow very quickly but are more difficult and expensive to construct and re-roof due to the need for specialized safety equipment.

Example Calculation

Let's say you are measuring a section of your attic to determine the roof pitch. You measure a horizontal distance (the run) of 48 inches. Over that distance, you measure that the roof height increases (the rise) by 16 inches.

To find the standard pitch ratio, you divide the rise by the run and multiply by 12:

(16 ÷ 48) x 12 = 4

Your roof has a 4/12 pitch. Using the calculator above, you would also find this equals an angle of approximately 18.4°.