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Roof Pitch Calculator

Calculate roof pitch, slope percent, roof angle, rafter length, and rafter length with optional overhang from rise and run.

Vertical roof rise in inches.

Horizontal roof run in inches.

Optional horizontal overhang in inches.

Status: initial

Results

Awaiting calculation

Roofing geometry

Introduction

The Roof Pitch Calculator converts rise and run into pitch, slope percent, angle, rafter length, and optional overhang-adjusted rafter length for early roofing and framing planning.

The calculator divides rise by run to find slope, multiplies that value by 12 to express pitch as x:12, converts the slope to an angle, and uses the Pythagorean theorem for rafter length.

Formula and method guide

Pitch x:12

Pitch = Rise / Run x 12

This gives the familiar roofing pitch format such as 4:12.

Slope percent

Slope Percent = Rise / Run x 100

A 4:12 roof is about 33.33% slope.

Roof angle

Angle = arctan(Rise / Run)

This converts roof pitch into degrees.

Rafter length

Rafter Length = sqrt(Rise^2 + Run^2)

This estimates the diagonal rafter line length before construction allowances.

Variables

Rise

The vertical height from the roof base line to the higher point.

Run

The horizontal distance from the wall line to the ridge or high point.

Pitch

The roof rise over a standard 12 inches of run.

Angle

The roof slope expressed in degrees.

Rafter length

The diagonal estimate from rise and run.

FAQs

What does this Roof Pitch Calculator calculate?
It calculates pitch x:12, slope percent, roof angle, rafter length, and rafter length with optional overhang.
What is roof pitch?
Roof pitch is roof steepness, often expressed as inches of rise for every 12 inches of run.
How do I calculate roof pitch?
Divide rise by run, then multiply by 12 to get the x value in x:12 pitch.
What is a 4:12 roof pitch?
A 4:12 roof rises 4 inches for every 12 inches of horizontal run.
How do I convert roof pitch to degrees?
Use the arctangent of rise divided by run.
How is slope percent calculated?
Slope percent equals rise divided by run, multiplied by 100.
How is rafter length calculated?
Rafter length is the square root of rise squared plus run squared.
Does this include roof overhang?
Yes, if you enter an optional horizontal overhang.
Is run the same as roof span?
No. For many simple gable roofs, run is half the total span.
Can this calculator design a roof?
No. It provides geometry estimates only, not structural design.
Does pitch affect roofing materials?
Yes. Roofing materials often have minimum slope requirements that must be checked.
Can I use feet instead of inches?
Yes if rise and run use the same unit, but output labels are written in inches for this version.
What is a low slope roof?
Low slope commonly refers to roofs below about 4:12, but product and code requirements vary.
What is a steep roof?
Roofs above about 9:12 are often treated as steep for access, safety, and fastening considerations.
Should I cut rafters from this result alone?
No. Verify site measurements, cuts, ridge details, overhang, code, and professional guidance first.

References

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