Roof Pitch Calculator

A roof’s pitch describes how steeply it rises over a horizontal distance. Knowing the pitch helps with roof planning, estimating rafter length, and communicating measurements. The Roof Pitch Calculator uses the roof’s rise and run to calculate its pitch ratio, angle, percentage, and rafter length.

What Is Roof Pitch?

Roof pitch is the vertical rise of a roof compared with its horizontal run. In the common X:12 format, the second number represents 12 inches of horizontal run. For example, a 6:12 roof rises 6 inches for every 12 inches horizontally.

Always measure rise and run in the same units. Roof pitch describes the slope; it is not the same as the roof’s angle in degrees.

How to Measure Roof Pitch

For a simple estimate, place a level horizontally and measure the vertical distance from the level to the roof surface at a known horizontal distance. If you measure over 12 inches, the vertical measurement is the rise for a standard X:12 pitch.

For example, a rise of 6 inches over a 12-inch run corresponds to a 6:12 pitch. Use appropriate fall protection and avoid walking on a roof unless it is safe to do so.

Roof Pitch Formulas

Pitch Ratio

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

To express the result in the common X:12 format:

$\text{X in X:12}=\frac{\text{Rise}}{\text{Run}}\times 12$

Roof Angle

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

Pitch Percentage

$\text{Pitch Percentage}=\frac{\text{Rise}}{\text{Run}}\times 100$

Example: Calculate a 6:12 Roof Pitch

Suppose the roof rises 6 inches over a 12-inch horizontal run.

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

$\text{Roof Pitch}=0.5\times 12=6:12$

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

$\text{Pitch Percentage}=\frac{6}{12}\times 100=50\%$

The roof pitch is 6:12, the angle is approximately 26.57°, and the pitch is 50%.

Roof Pitch Reference Chart

The chart below uses a 12-inch horizontal run for each pitch. The angle and percentage are approximate.

“Low,” “moderate,” and “steep” are general descriptions, not universal classifications. Roofing material requirements and minimum pitch can vary, so check the product instructions and local building requirements for your project.

How to Calculate Rafter Length

For a simple roof section, the rafter length from the wall line to the ridge is the hypotenuse of a right triangle:

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

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

$\text{Rafter Length}=\sqrt{6^2+{12}^2}$

$\text{Rafter Length}=\sqrt{36+144}=\sqrt{180}\approx 13.42\text{ ft}$

The rafter length is approximately 13.42 feet, before accounting for overhangs, cuts, or other framing details.

Accounting for an Overhang

If the overhang measurement is taken along the sloped roof surface, add it to the calculated rafter length:

$\text{Rafter Length with Overhang}=\text{Rafter Length}+\text{Overhang Along Roof}$

If the overhang is measured horizontally, calculate its sloped length using the same pitch before adding it. Do not add a horizontal overhang directly to the sloped rafter length.

Why Roof Pitch Matters

Roof pitch can affect roof drainage, usable attic space, roof appearance, and the choice or installation of roofing materials. It can also help estimate the sloped roof surface and rafter dimensions. A pitch calculation is a measurement aid—not a substitute for structural design, manufacturer instructions, or local code requirements.

FAQs

What does a 4:12 roof pitch mean?

It means the roof rises 4 inches for every 12 inches of horizontal run. Its angle is approximately 18.43°.

How do I convert roof pitch to degrees?

Divide the rise by the run, then take the inverse tangent:

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

Use the same units for rise and run.

Is roof pitch percentage the same as roof angle?

No. Pitch percentage is rise divided by run, multiplied by 100. Roof angle is measured in degrees using the arctangent of rise divided by run.

Does the rafter length include the overhang?

Not automatically. The basic formula calculates the length for the entered rise and run. Add the overhang separately, making sure it is measured along the roof slope—or convert a horizontal overhang to its sloped length first.

Can roof pitch determine which roofing material to use?

It can help narrow down suitable materials, but each product has its own installation requirements and minimum pitch. Check the manufacturer’s instructions and applicable local building codes.