How to Calculate Roof Pitch

Roof pitch answers a deceptively simple question: how steep is this roof? It matters far beyond aesthetics. Pitch determines which roofing materials will work, how well rain and snow shed, how much surface area you need to cover, and how safely you can walk on it. Roofers and builders express it in a few interchangeable ways, and it's worth knowing how to move between them.

Roof pitch is fundamentally a slope: a ratio of how much the roof rises vertically for how much it runs horizontally. Because the tradition of framing lumber makes a 12-inch run convenient to work with, pitch is most often stated as rise per 12 inches of run — a "6/12 roof" rises 6 inches for every 12 inches it runs across horizontally.

The three ways to say it

1. Pitch ratio (X-in-12) — rise per 12 inches of run. The roofer's default.
2. Angle in degrees — the roof's angle measured from horizontal.
3. Percent grade — rise ÷ run × 100. Common in engineering and European contexts.

They all describe the same steepness; which one you use depends on who you're talking to.

The math

Ratio = rise ÷ run              (scaled so run = 12)
Angle = arctan(rise ÷ run)      in degrees
Grade = (rise ÷ run) × 100%

All three derive from two measurements: the rise (vertical change) and the run (horizontal distance).

Worked example

A roof rises 6 inches over a 12-inch run:

Ratio = 6-in-12
Angle = arctan(6 ÷ 12) ≈ 26.6°
Grade = (6 ÷ 12) × 100 = 50%

So a 6/12 roof is about a 26.6° slope and a 50% grade. All three numbers describe the identical roof.

What pitches mean in practice

Different steepness suits different materials and purposes:

Pitch	Angle	Typical use
2/12–4/12	9–18°	Low slope — needs special low-slope roofing
4/12–9/12	18–37°	Standard asphalt shingles
9/12–12/12	37–45°	Steep — dramatic look, harder to walk
12/12+	45°+	Very steep — sheds snow well, costly to build

The trade-off is classic roofing physics: a steeper roof sheds rain and snow far better, but it costs more to build, covers more surface area, and is more dangerous to walk on. Low-slope roofs are cheaper and more walkable but need waterproofing designed for standing water.

Measuring rise and run

To compute pitch yourself, measure the rise over a known run:

• Choose a convenient horizontal distance (often 12 inches, or a full foot) along the roof.
• Measure the vertical rise over that run.
• Keep the units consistent, and scale the run to 12 for the standard ratio.

If you can't access the roof safely, it's often easier to measure inside an attic or from a gable end, where you can see the framing triangle directly.

Key takeaways

• Pitch is a slope: ratio (X-in-12), degrees, or percent grade.
• 6/12 = 26.6° = 50% — all the same roof.
• Steeper sheds water better but costs more and is harder to work on.
• Measure rise and run consistently, scale run to 12 for the standard ratio.

FAQ

What's the difference between pitch and slope? In everyday roofing, pitch and slope are used interchangeably to mean steepness. Strictly, some builders define "slope" as rise/run and "pitch" as rise per 12, but for practical purposes they describe the same roof.

How do I convert pitch to degrees? Use the inverse tangent: degrees = arctan(rise ÷ run). A 6/12 roof is arctan(0.5) ≈ 26.6°.

What pitch is best for rain and snow? Generally, steeper pitches shed snow and rain better — roughly 4/12 and up shed well. Very steep roofs (>12/12) are excellent for snow shedding but expensive.

Can I estimate pitch without getting on the roof? Yes — measure from inside an attic or the gable end where you can see the rafter triangle, using a level and a tape measure.

Convert your measurement with the Roof Pitch Calculator, and estimate the surface area of your roof with the Square Footage Calculator.