Roof Pitch Calculator

Frequently Asked Questions

What is roof pitch and how is it expressed?

Pitch is rise over run, written as "X:12" - meaning X inches of vertical rise for every 12 inches of horizontal run. A 6:12 roof rises 6 inches per foot of horizontal travel, equivalent to a 26.57° angle and a 50% slope.

How do I convert pitch to angle and slope percentage?

Angle = arctan(rise ÷ run). Slope % = (rise ÷ run) × 100. Common pitches: 4:12 = 18.4° (33% slope), 6:12 = 26.6° (50%), 8:12 = 33.7° (67%), 12:12 = 45° (100%).

What pitch is required for different roofing materials?

Asphalt shingles need a minimum 2:12 (with double underlayment to 4:12, standard above). Standing seam metal works down to 1:12 (sometimes 1/4:12). Most clay/concrete tile requires 4:12 minimum. Below 2:12, you generally need a fully adhered membrane (EPDM, TPO, modified bitumen) - it is functionally a flat roof.

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How This Calculator Works

In US residential construction, roof pitch is universally expressed as rise over run - how many inches the roof rises vertically for every horizontal foot (12 inches) it travels. A "6:12" pitch means the roof rises 6 inches for every 12 inches of horizontal distance. Enter your measured rise and run (in inches), and the calculator normalizes the result to the standard X:12 format and also gives you the slope as a percentage and an angle in degrees.

Pitch Categories & What They Mean

Low-slope (under 4:12, less than 18°): Sometimes called "flat" but never truly flat (water needs to drain). Requires special membrane roofing - EPDM, TPO, modified bitumen, or built-up roofing - because asphalt shingles cannot shed water at this angle without leaking. Common on commercial buildings, modern homes, sheds, and porch roofs.

Conventional (4:12 to 9:12, ~18° to 37°): The "Goldilocks" range for asphalt shingles, metal panels, tile, and most other standard roofing materials. Sheds water and snow well, walkable for repairs, and the most common pitch range in American homes.

Steep (over 9:12, more than 37°): Looks dramatic, sheds snow aggressively, and adds attic volume. Requires roof jacks, harnesses, or scaffolding for any work. Often seen on Victorian, Tudor, and chalet-style architecture.

How to Measure Pitch From the Ground

You don't have to climb on the roof. There are three common methods:

Level + tape: Hold a 12-inch level horizontally against the underside of a rafter or against the gable end. Measure the vertical distance from the level's far end down to the rafter - that's your rise per 12 inches of run.

Smartphone app: Most phones have an inclinometer in the Measure app or compass app. Place the phone flat against the rafter or shingle face to read the angle directly. Convert: rise = 12 × tan(angle).

Gable photo: Take a perfectly perpendicular photo of the gable end and measure the rise and run in the photo. Ratios are preserved by photography.

Why Pitch Matters

Material choice: Asphalt shingles are rated for 4:12 minimum (some specialty shingles down to 2:12 with extra underlayment). Metal panels can go lower. Wood shake needs 4:12 or steeper.

Snow load: Steep roofs shed snow on their own; low-slope roofs accumulate it and must be engineered for the local snow load (often 30–50 psf in northern climates).

Wind resistance: Steeper roofs catch more wind. The optimum pitch for hurricane-zone homes is typically 4:12 to 6:12.

Attic space: A 12:12 pitch over a 30-foot-wide house gives ~15 feet of attic peak height - useful for storage or a future loft conversion.

Cost: Steeper roofs use more material per square foot of footprint (more area to cover) and are more expensive to install due to safety requirements.

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