Roof Pitch Calculator

Overview

How to use this calculator

1. Measure the vertical rise and horizontal run of your roof segment. For existing roofs, you can do this over a convenient distance, such as 12 inches, using a level and tape measure.
2. Enter the rise and run in the same units into the calculator.
3. Review the pitch (in 12), slope percentage, and angle in degrees.
4. Use the pitch and angle outputs when setting framing squares, saw bevels, and when communicating slope requirements to suppliers or inspectors.

Inputs explained

Rise

The vertical change in height over the measured run. In roofing, this is usually measured in inches over a horizontal run of 12 inches when describing standard pitches like 4/12 or 8/12.

Run

The horizontal distance over which the rise occurs. For pitch notation, 12 inches of run is standard, but you can measure over any convenient distance as long as rise and run use the same units.

Outputs explained

Pitch (in 12)

The roof pitch expressed as inches of rise over 12 inches of run—for example, a result of 6 means a 6/12 pitch. This is the format most shingle wrappers, codes, and framing references use.

Slope (%)

The slope of the roof expressed as a percentage, calculated as (rise ÷ run) × 100. A 4/12 pitch corresponds to roughly a 33.3% slope.

Angle (degrees)

The roof angle relative to horizontal in degrees. This is the bevel angle you can set on a miter saw, digital angle finder, or bevel gauge for plumb cuts on rafters, fascia, and other roof components.

When to use it

• Checking whether an existing or planned roof meets minimum slope requirements for asphalt shingles, metal panels, or low-slope roofing systems.
• Setting saw bevels and framing square settings for plumb cuts, birdsmouth cuts, fascia, and barge rafters.
• Communicating roof slope clearly to suppliers, engineers, inspectors, and installers using common pitch notation and angles.
• Converting between different ways of describing slope (pitch, percent, degrees) when reading plans, manufacturer specs, or local building codes.
• Helping DIYers and new carpenters visualize what a 4/12, 6/12, or 12/12 roof looks like in terms of steepness and safety considerations.

Tips & cautions

• Keep units consistent: if you measure rise in inches, measure run in inches too. The ratio is what matters; mixed units will distort the results.
• To measure an existing roof, place a level along the roof surface, mark a 12-inch horizontal run, and then measure the vertical rise from the level to the roof at that mark.
• If all you know is the pitch (for example, 7/12 from a plan), enter rise = 7 and run = 12 to see the corresponding slope percentage and angle.
• For safety and material performance, always consult manufacturer documentation for minimum and maximum allowable slopes before installing roofing materials.
• Use the angle output to set your saw or digital angle finder, but double-check fit with test cuts on scrap material before committing to a full run of rafters or fascia.
• This calculator does not size rafters, ceiling joists, or structural elements; it is focused solely on geometry (pitch, slope, and angle).
• It does not account for overhangs, ridge thickness, seat cuts, or heel heights; those require separate framing calculations or references.
• Complex roofs with hips, valleys, or multiple pitches require separate measurements and calculations for each plane or transition.
• Minimum and maximum slope requirements for specific roofing products depend on local code, climate, and manufacturer instructions; this tool does not enforce those limits.

Worked examples

Deep dive

FAQs

How do I use the angle output for rafter cuts?

The angle output is the roof angle relative to horizontal. For plumb cuts at the top of rafters, you set your saw to that angle. For seat cuts (birdsmouth), you may need complementary angles and framing references; consult a rafter layout guide for specifics.

Is pitch the same as slope percentage?

They describe the same roof steepness but in different formats. Pitch is inches of rise over 12 inches of run (for example, 6/12), while slope percentage is rise divided by run expressed as a percent. A 6/12 pitch is roughly a 50% slope.

Can I enter metric measurements like centimeters or meters?

Yes. As long as rise and run use the same unit, the ratio is unitless and the resulting pitch, slope percentage, and angle will be correct. Just interpret the pitch result as rise per 12 units of run instead of strictly 12 inches.

What pitch do asphalt shingles or metal roofs require?

Requirements vary by product and manufacturer, but many asphalt shingles are rated down to 2/12–4/12 with special underlayment, and metal panels often have their own minimum slopes. Always check current manufacturer specifications and local building code instead of relying on rules of thumb.

Does this calculator account for ridge thickness or birdsmouth seat cuts?

No. It focuses on geometric relationships between rise, run, and angle. Adjustments for ridge thickness, heel height, and birdsmouth cuts are framing details that should be handled with rafter tables, layout guides, or structural design documents.

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