Roof pitch affects nearly every part of a roofing project. It influences how water drains, the type of materials you can use, how much ventilation is needed, and even how the finished structure looks from the street.

This calculator helps you measure roof pitch by using the rise and run of the roof, then converts those numbers into degrees, percentage, and rafter length.

The guide below explains how roof pitch works and how the calculator turns your measurements into clear, useful results.

What Roof Pitch Represents

Roof pitch describes the steepness of a roof. It is usually expressed in one of three ways:

• pitch as a ratio, such as 4 in 12
• pitch as a degree measurement
• pitch as a percentage

Each format shows the same information in a different style. A roof with a rise of 4 inches for every 12 inches of run is a 4 in 12 roof. That same slope can be expressed as a degree angle or as a percentage grade.

Understanding these formats helps you communicate with contractors, select materials, and plan your project more precisely.

How Roof Pitch Is Calculated

The basics are simple. The rise is the vertical height of the roof. The run is the horizontal distance over which that rise occurs. Once you know both measurements, you can calculate pitch.

Pitch ratio uses the rise and run directly.

Degree pitch uses trigonometric functions to convert slope into an angle.

Percentage pitch uses rise divided by run multiplied by one hundred.

The calculator handles all of these conversions once you enter the rise and run.

Calculating Rafter Length

Rafter length is determined by the rise and run using the Pythagorean theorem. This is because the rise, run, and rafter form a right triangle.

The calculator measures the diagonal side of that triangle, which is the actual length of the rafter from the top plate to the ridge.

Rafter length helps you determine how much lumber to buy and how the roof should be framed. It also helps with estimating sheathing, roofing material, and even overhangs.

Why Roof Pitch Matters

Pitch is more than a simple measurement. It influences several practical aspects of a roof.

A lower pitch roof is easier to walk on and often uses simpler framing. It may require additional waterproofing because water drains more slowly.

A higher pitch roof sheds water more effectively and provides more attic space, but it can be more expensive to build due to the added materials and labor. Steeper roofs may also require shingles or roofing materials rated for the angle.

Pitch also affects snow load, wind performance, ventilation, and overall structural demands.

For these reasons, many local building codes specify minimum pitches for certain roofing materials.

Common Roof Pitch Examples

Here are a few examples to show how typical measurements translate.

Example 1

• Rise: 4 inches
• Run: 12 inches
• Pitch ratio: 4 in 12
• Roof angle: about 18.4 degrees
• Pitch percentage: about 33 percent

Example 2

• Rise: 6 inches
• Run: 12 inches
• Pitch ratio: 6 in 12
• Angle: about 26.6 degrees
• Percentage: 50 percent

Example 3

• Rise: 9 inches
• Run: 12 inches
• Pitch ratio: 9 in 12
• Angle: about 36.9 degrees
• Percentage: 75 percent

The calculator converts your measurements into all three formats instantly.

Tips for Measuring Roof Pitch Accurately

A few simple habits help improve accuracy.

• Measure the rise and run carefully. Even a small error affects the calculated angle and rafter length.
• If you cannot measure directly on the roof, measure inside the attic from the top of the rafter to the bottom chord. The rise and run remain the same.
• Use a long enough level or straightedge to get a clear measurement of both rise and run.
• Check local building codes to ensure the pitch meets requirements for your roofing material.

Why This Calculator Helps

Roof pitch is easy to understand once you know the basics, but doing the math by hand takes time.

The calculator gives you pitch ratio, degrees, percentage, and rafter length from a simple set of measurements. It streamlines planning, estimating materials, and reviewing construction details.

Try the Calculator

Enter the rise and run of the roof. The calculator shows the pitch, angle, percentage grade, and estimated rafter length.

Use the results to plan your roofing project with confidence and accuracy.