Roof Pitch Calculator calculates the slope or angle of your roof. Simply input your roof's run and rise values, and it will convert the roof pitch into degrees and percentages while also determining the rafter length.

What is Roof Pitch?

Roof pitch is the slope or angle of a roof. It is typically expressed as a ratio that compares the vertical rise of the roof to its horizontal run. For example, a pitch of 4:12 means that for every 12 units of horizontal run, the roof rises 4 units vertically.

How to Calculate Roof Pitch?

Calculating roof pitch is a simple process that involves measuring the slope of your roof. Roof pitch is typically expressed as the ratio of the roof’s vertical rise to its horizontal run, often written as “X:12.” For example, a pitch of 4:12 means the roof rises 4 inches for every 12 inches of horizontal distance.

Here’s a step-by-step guide to calculate roof pitch:

1. Measure the Run: Place the level horizontally on the roof, ensuring one end touches the surface. Mark a point exactly 12 inches from the edge where the level meets the roof.
2. Measure the Rise: From the marked 12-inch point, measure vertically to the roof’s surface. This measurement is your roof's rise.
3. Calculate the Pitch: Express the rise measurement as a ratio to the 12-inch run. For instance, if the rise is 6 inches, your roof pitch is 6:12

Roof Pitch Formula

1. Pitch Ratio Formula

The pitch ratio, also known as the roof pitch or roof slope, describes the steepness of a roof. The pitch ratio is typically written as a fraction (e.g., 1/4, 4/12) or sometimes as a ratio (e.g., 1:4). The first number (numerator) represents the rise, and the second number (denominator) represents the run.

To find the roof pitch ratio you have to divide the rise by the run. This is the most basic formula for roof pitch:

$\text{Pitch Ratio}=\frac{\text{Rise}}{\text{Run}}$

For example, if the rise is 6 inches and the run is 12 inches:

$\text{Pitch Ratio}=\frac{6}{12}=0.5$

2. Roof Pitch in Degrees

It refers to expressing the steepness of a roof as an angle measured in degrees, rather than as a ratio of rise to run (like 4/12 or 6/12). This angle is formed between the roof surface and a horizontal plane.

To convert the pitch ratio into degrees, use the following formula:

$\theta =arctan\left(\frac{\text{Rise}}{\text{Run}}\right)$

For example, if the rise is 6 inches and the run is 12 inches:

$\theta =arctan\left(\frac{6}{12}\right)=arctan\left(0.5\right)\approx {26.57}^{\circ }$

3. Roof Pitch as a Percentage

It is another way to express the steepness of a roof. It represents the ratio of the roof's rise to its run, multiplied by 100 to get a percentage value. Using percentages is just another way to describe the slope of a roof.

To express roof pitch as a percentage:

$\text{Pitch Percentage}=\left(\frac{\text{Rise}}{\text{Run}}\times 100\right)$

For example, if the rise is 6 inches and the run is 12 inches:

$\text{Pitch Percentage}=\left(\frac{6}{12}\times 100\right)=50\%$

What Is Rafter Length?

Rafter length is the measurement of the sloping beam (rafter) that spans from the ridge of the roof (the peak) to the edge or eaves of the roof. It is an essential dimension in roof construction, as it determines the size of the rafters needed to support the roof structure effectively.

How to Calculate Rafter Length

Rafter length can be calculated using the Pythagorean theorem

Formula for Rafter Length

$\text{Rafter Length}=\sqrt{\left(Ris{e}^2+Ru{n}^2\right)}$

Example Calculation

If the rise is 6 feet and the run is 12 feet:

$\text{Rafter Length}=\sqrt{\left(6^2+{12}^2\right)}$

$\text{Rafter Length}=\sqrt{\left(36+144\right)}$

$\text{Rafter Length}=\sqrt{180}\approx 13.42\text{feet}$

Adjusting for Overhang

If the roof has an overhang, you need to add this extra length to the calculated rafter length. For example, if the overhang is 2 feet, the total rafter length will be:

$\text{Total Rafter Length}=\text{Rafter Length}+\text{Overhang}$

Example with Overhang:

$\text{Total Rafter Length}=13.42+2=15.42\text{feet}$

What Is a Roof Pitch Chart?

A roof pitch chart is a reference tool that visually represents the relationship between the rise and run of a roof, allowing you to determine its slope or steepness. Roof pitch is typically expressed as a ratio, such as 4:12, which means the roof rises 4 inches for every 12 inches of horizontal run. A roof pitch chart simplifies this information by presenting it in a clear and easy-to-understand format.

Roof Pitch Chart

How to Use a Roof Pitch Chart

1. Identify the Rise and Run: Measure the vertical rise and horizontal run of your roof.
2. Locate Your Pitch: Find the corresponding pitch ratio in the chart (e.g., 6:12 for a 6-inch rise and 12-inch run).
3. Interpret the Data: Use the chart to determine the pitch angle (in degrees) or pitch percentage.

Practical Applications of Roof Pitch

Understanding roof pitch is crucial for various reasons:

• Material Calculation: Determines the amount of roofing material required.
• Drainage Efficiency: A steeper pitch allows for faster and more efficient drainage, minimizing the risk of leaks and ice dams.
• Building Codes: Some areas mandate minimum roof pitch for safety.

Aesthetic Design: Influences the architectural appearance of the building.