How do I calculate roof pitch from rise and run?

Divide the vertical rise by the horizontal run, then multiply by 12. A roof that rises 6 inches over a 12-inch run has a 6/12 pitch.

What angle is a 6/12 roof pitch?

A 6/12 roof pitch is approximately 26.57 degrees. Its slope is 50%, and its roof-area multiplier is approximately 1.1180.

Is roof pitch the same as roof slope?

They describe the same incline in different formats. Pitch is commonly written as rise over 12 inches of run, while slope may be expressed as a percentage or angle in degrees.

What is a roof pitch multiplier?

The multiplier converts a level horizontal footprint into sloped roof area. Multiply the horizontal roof area by the pitch multiplier to estimate the corresponding sloped surface area.

Can this calculator size rafters or roof trusses?

No. It calculates geometry only. Structural member sizes depend on span, loads, species, grade, spacing, connections and local building requirements and should be verified by a qualified professional.

Four measurement methods

Roof Pitch Calculator

Convert pitch, rise and run, roof angle, or building span into the measurements you need: x/12 pitch, degrees, slope percentage, area multiplier and rafter line.

US roofing format

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What measurement do you have?

Rise for every 12 inches of runin / 12

Example: enter 6 for a standard 6/12 roof.

Your result

6/12

Moderate pitch

Roof angle

26.57°

Angle above the horizontal run

Slope percentage

50%

Vertical rise divided by horizontal run

Area multiplier

1.1180

Multiply a level footprint by this factor

Rafter line

13.416

Length for each 12 units of horizontal run

Planning note: This result describes roof geometry. It does not determine structural member sizes, code compliance, or whether a roof is safe to build.

What your roof-pitch result means

A pitch such as 6/12 means the roof rises 6 inches for every 12 inches of horizontal run. The same incline can also be stated as 26.57° or a 50% slope. These are different ways of describing one roof angle.

Pitch

rise ÷ run × 12

Produces the familiar x/12 roofing format.

Angle

tan⁻¹(rise ÷ run)

Expresses the incline in degrees.

Multiplier

√(1 + slope²)

Converts plan area to sloped surface area.

Quick reference

Roof pitch chart

Compare common x/12 pitches with their angles, percentages, and area multipliers. Select a pitch to open the calculator with that value.

Pitch	Degrees	Slope	Multiplier	Open calculator
2/12	9.46°	16.67%	1.0138	Calculate
3/12	14.04°	25%	1.0308	Calculate
4/12	18.43°	33.33%	1.0541	Calculate
5/12	22.62°	41.67%	1.0833	Calculate
6/12	26.57°	50%	1.1180	Calculate
7/12	30.26°	58.33%	1.1577	Calculate
8/12	33.69°	66.67%	1.2019	Calculate
9/12	36.87°	75%	1.2500	Calculate
10/12	39.81°	83.33%	1.3017	Calculate
12/12	45°	100%	1.4142	Calculate

How to measure roof pitch

1Place a level horizontally against a rafter or roof surface.
2Mark a 12-inch horizontal run on the level.
3Measure vertically from that mark to the roof surface.
4Enter that rise as the x value in an x/12 pitch.

Safer measurement option

When possible, measure from an accessible attic rafter or use reliable building plans. Avoid climbing onto a roof solely to obtain a pitch measurement.

Wet, icy, damaged, or steep roofs require appropriate fall protection and professional judgment.

Common roof-pitch mistakes

Using roof width as run

For a symmetrical gable roof, the run is usually half the full building span—not the full width.

Measuring along the rafter

Run is horizontal. The diagonal rafter line is the hypotenuse and produces a different ratio.

Mixing measurement units

Rise and run must use the same unit before they are divided. Inches with inches or feet with feet both work.

Ordering from footprint alone

A level footprint excludes the extra surface created by roof slope, overhangs, waste, hips and valleys.