Roof Pitch Calculator

Introduction

A roof pitch calculator helps you figure out the steepness of a roof. Roof pitch is the angle or slope of your roof, and it is usually shown as a ratio like 6/12. This means the roof rises 6 inches for every 12 inches it runs horizontally. Knowing your roof pitch is important for many reasons. It helps you pick the right roofing materials, estimate how many shingles you need, and plan for proper water drainage. Getting the pitch right matters when you build a new roof or replace an old one. Use this simple tool to calculate your roof pitch quickly by entering your rise and run measurements.

How to Use Our Roof Pitch Calculator

Enter your roof's rise and run measurements below. The calculator will give you the roof pitch as a ratio, angle in degrees, and slope percentage.

Rise: Type in how many inches your roof goes up vertically. This is the height from the top of the wall to the peak of the roof. You can measure this from inside your attic by holding a level flat and measuring straight up from it to the underside of the roof.

Run: Type in how many inches your roof covers horizontally. This is the flat distance from the outside edge of the wall to the point directly below the roof's peak. A standard run is usually measured over 12 inches, but you can enter any length you have.

Unit: Choose whether you are entering your measurements in inches, feet, or centimeters. Make sure both the rise and run use the same unit so the result is correct.

Understanding Roof Pitch

Roof pitch is the steepness or slope of a roof. It tells you how much a roof rises for every foot it runs horizontally. For example, a 6/12 pitch means the roof goes up 6 inches for every 12 inches it goes across. This measurement is important for anyone building, repairing, or replacing a roof.

Why Roof Pitch Matters

The pitch of your roof affects many things. A steeper roof sheds rain and snow more easily, which helps prevent leaks and water damage. A flatter roof is easier and safer to walk on but may hold water if not properly drained. The pitch also determines what roofing materials you can use. For instance, asphalt shingles typically need a minimum pitch of 4/12, while metal roofing can work on lower slopes.

How Roof Pitch Is Measured

Roof pitch is written as a ratio, like rise over run. The "rise" is how many inches the roof goes up vertically. The "run" is always measured over 12 inches of horizontal distance. So a "4/12 pitch" means the roof rises 4 inches for every 12 inches of horizontal run. You can also express pitch as a degree angle or as a percentage.

Common Roof Pitch Ranges

Low pitch (1/12 to 3/12): Nearly flat roofs, often found on commercial buildings or modern homes. These require special waterproof membranes.
Medium pitch (4/12 to 8/12): The most common range for residential homes. These work well with most roofing materials.
Steep pitch (9/12 and above): Found on older homes, A-frames, and certain architectural styles. These roofs shed water and snow very well but cost more to build and maintain.

How Roof Pitch Affects Cost

A steeper roof costs more to install because it requires more materials, extra safety equipment, and more labor time. Roofers often charge higher rates for steep-pitch work due to the added danger. Knowing your roof's pitch before getting quotes helps you budget accurately and compare bids from different contractors.

Formulas used

Rafter Length (Pythagorean Theorem)

\text{Rafter} = \sqrt{\text{Rise}^2 + \text{Run}^2}

Slope in Degrees

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

Slope as Percentage

\text{Slope\%} = \frac{\text{Rise}}{\text{Run}} \times 100

Pitch (x:12)

x = \frac{\text{Rise}}{\text{Run}} \times 12

Run from Rafter and Pitch Ratio

\text{Run} = \frac{\text{Rafter}}{\sqrt{1 + \left(\frac{\text{Rise}}{\text{Run}}\right)^2}}

Frequently asked questions

What is roof pitch?

Roof pitch is how steep your roof is. It is shown as a ratio like 6:12, which means the roof rises 6 inches for every 12 inches of horizontal run. A higher first number means a steeper roof.

How do I measure the rise of my roof?

Go into your attic and hold a level horizontally. Measure straight up from the level to the underside of the roof deck. That vertical distance is your rise. You can also measure from the top of the exterior wall plate up to the ridge board.

How do I measure the run of my roof?

The run is the horizontal distance from the outside edge of the wall to the point directly below the ridge (peak) of the roof. It is half the total span of the building. You can measure this from inside the attic along your level.

What is the difference between roof pitch and roof slope?

They are closely related but expressed differently. Pitch is written as a ratio like 6:12. Slope can be shown in degrees (the angle from horizontal) or as a percentage (rise divided by run times 100). This calculator converts between all three formats.

Can I use different units for rise and run?

Yes. Each field has its own unit selector. You can enter rise in inches and run in feet, for example. The calculator converts everything internally so your results will be correct no matter what units you mix.

How is rafter length calculated?

Rafter length is calculated using the Pythagorean theorem: Rafter = √(Rise² + Run²). This gives you the sloped distance from the eave (bottom edge) to the ridge (peak) of the roof.

What does the walkability scale mean?

The walkability scale shows how safe it is to walk on a roof at that pitch. A low pitch near 0° is easy to walk on. As the pitch gets steeper, it becomes harder and more dangerous. Roofs above about 8:12 usually need safety harnesses and roof jacks.

What roof pitch is best for my area?

Areas with heavy snow or rain do better with steeper pitches (6:12 or higher) because water and snow slide off faster. Dry, warm climates can use lower pitches. Always check your local building codes for minimum pitch requirements.

What is the most common roof pitch for homes?

The most common residential roof pitch in the United States is between 4:12 and 6:12. A 4:12 pitch rises 4 inches for every 12 inches of run. This range works well with most roofing materials and provides good water drainage.

What is the minimum pitch for asphalt shingles?

Most asphalt shingle manufacturers require a minimum pitch of 2:12, and some require 4:12 for standard installation. Between 2:12 and 4:12, you usually need a special underlayment beneath the shingles. Always check the manufacturer's instructions.

How do I convert roof pitch to degrees?

Use the formula: degrees = arctan(pitch ÷ 12). For example, a 6:12 pitch equals arctan(6 ÷ 12) = 26.57°. You do not need to do this math yourself. Just enter the pitch in this calculator and it shows the degrees automatically.

How do I convert roof pitch to a percentage?

Divide the rise by the run and multiply by 100. For a 6:12 pitch: (6 ÷ 12) × 100 = 50%. This calculator does the conversion for you when you enter any two values.

Does rafter length include the eave overhang?

No. The rafter length shown here is only the distance from the wall plate to the ridge. If your roof has an overhang (eave), you need to add that extra length separately. Measure the horizontal overhang and use the same pitch to calculate the additional rafter length.

What pitch is considered a flat roof?

A roof with a pitch of 2:12 or less is generally considered a flat or low-slope roof. These roofs need special waterproof membrane systems like built-up roofing, TPO, or EPDM because standard shingles cannot prevent leaks at such low angles.