How to Measure Roof Pitch: 3 Safe Methods With a Level

How to measure roof pitch: hold a level horizontal against the underside of a rafter in the attic, measure 12 inches along the level, then measure straight up from that mark to the rafter. That vertical number is the rise per 12 inches of run, so 6 inches means a 6/12 pitch.

You can do the same from a ladder at the eave, or use a phone app.

How to measure roof pitch: what the numbers mean

Roof pitch compares vertical rise to horizontal run, written as rise over 12. A 6/12 roof rises 6 inches for every 12 inches it runs. Pitch matters for choosing shingles, ordering material, drainage, walkability and safety.

Quick facts: how to measure roof pitch
Formula	Pitch = rise (inches) over 12 inches of run
Tools	Level, tape measure, pencil; a phone inclinometer app also works
Safest place	From the attic or the ground, not a steep roof
Low-slope roof	Below about 2/12, which needs special roofing

Method 1: from the attic

1. Find a rafter or truss in the attic that is easy to reach.
2. Hold a level against the underside of the rafter so the bubble is centered.
3. Mark 12 inches along the level from the point where it touches the rafter.
4. Measure straight down or up to the rafter from that 12-inch mark. That distance is the rise.
5. Write it as rise/12.

Method 2: from a ladder at the eave

Lean a ladder safely, hold a level on the roof surface so it is horizontal, mark 12 inches and measure the vertical distance to the shingles. Do not step onto the roof. Use another person to hold the ladder.

Method 3: with a phone app

Hold the phone along the roof slope from the ground or lay it on the rafter in the attic. An inclinometer app shows the angle, which you can convert with the chart below. It is quick, and good enough for a rough estimate.

Pitch and angle chart

Pitch	Angle	Description
2/12	9.5°	Low slope
4/12	18.4°	Common, walkable
6/12	26.6°	Moderate
8/12	33.7°	Steep
12/12	45°	Very steep

Why pitch matters

Shingles have a minimum pitch for proper drainage. Metal and membrane roofs suit low slopes. Steeper roofs shed water and snow quickly but are harder and riskier to work on and use more material. Insurers and roofers may charge more or have safety rules for steep roofs.

Common mistakes

Measuring on a sagging or uneven spot, not holding the level horizontal, mixing up rise and run, and measuring a skylight curb or dormer instead of the main roof all cause errors. Measure two or three places and use the most common value.

Safety first

Never walk a wet, icy, mossy or steep roof. Use the attic or the ground, wear shoes with grip and a harness if you must go up, and avoid working alone. For roofs above one story or steeper than about 7/12, a roofer should handle it.

Worked example

Suppose you hold a level against a rafter, mark 12 inches along it and measure 8 inches straight up to the rafter. The pitch is 8/12. Dividing 8 by 12 gives 0.667, and the inverse tangent of that is about 33.7 degrees. To find the surface multiplier, take the square root of 12 squared plus 8 squared, then divide by 12, which is about 1.20. So 1,000 square feet of footprint needs about 1,200 square feet of roofing.

Check your result

Measure in two or three places and compare. Rafters can bow or be notched, and a single odd reading is not reliable. If your readings differ by more than half an inch of rise, trust the most common one, or have a roofer confirm. Doing it twice is the surest way to learn how to measure roof pitch accurately.

When to call a professional

A roofer can measure pitch, check the surface area and advise on materials. Knowing how to measure roof pitch helps you ask good questions and understand quotes, but a professional is the safer way to check a steep or high roof.

Related reading

• How Many Bundles of Shingles in a Square? Easy Roof Math
• Roof replacement cost per square foot: What Drives the Price and How to Get a Fair Quote
• Metal Roof vs Shingles: Cost-Free Comparison of What Matters
• How to Repair a Flat Roof Leak: Find It, Patch It, Prevent Ponding

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