How do I measure roof pitch?

Measure the vertical rise over a 12-inch horizontal run; that's the x:12 pitch.

What does a 6:12 roof pitch mean?

The roof rises 6 inches for every 12 inches across, about 26.6°.

How do I convert roof pitch to degrees?

Take the inverse tangent (arctan) of the rise divided by the run.

How to Measure Roof Pitch

Published 7/22/2025 · 3 min read · Everyday calculators

Marco Bianchi — Home, DIY & motoring writer at OneKitly

Renovation · Materials

Checked against 2 sources

View profile →

In short

Roof pitch is how steep a roof is, given as a ratio of vertical rise to horizontal run — often 'rise over 12', like 6:12. To measure it, hold a level horizontally against the roof, mark 12 inches along it, and measure straight down to the roof at that point: that drop in inches is the rise. A 6-inch drop over 12 is a 6:12 pitch, roughly a 26.6° angle.

New timber roof trusses against open sky. — Saeed Khokhar · Pexels · Pexels

Roof pitch is rise over run, like 6:12. Here's how to measure it with a level, how to convert it to an angle or percentage, and why it matters.

What roof pitch is

Roof pitch describes how steeply a roof slopes, and it's usually written as a ratio of rise to run: how many units the roof climbs vertically for a fixed horizontal distance. That fixed distance is conventionally 12, so a '6:12' pitch rises 6 for every 12 across. A low number like 2:12 is a nearly flat, shallow roof; a high one like 12:12 is a steep 45-degree slope. The convention lets builders describe any roof's steepness with a single, comparable pair of numbers.

Measuring it with a level

You can measure pitch with just a spirit level and a tape measure — often from inside the loft, against a rafter, which is safer than climbing on the roof. Hold the level dead horizontal with one end touching the roof surface, measure 12 inches along it, and from that 12-inch mark measure straight down to the roof. That vertical distance is the rise. If it's 6 inches, the pitch is 6:12; if it's 4 inches, it's 4:12. The horizontal 12 is fixed, so only the drop changes.

Pitch as an angle or percentage

The rise:run ratio can be turned into other units. For an angle in degrees, take the inverse tangent (arctan) of rise divided by run: a 6:12 pitch is arctan(6/12) = arctan(0.5) ≈ 26.6°, and 12:12 is arctan(1) = 45°. For a percentage, divide rise by run and multiply by 100, so 6:12 is 50%. Roofers tend to use rise:12, engineers often prefer degrees, and road-style signs use percent — same slope, three ways of saying it.

Why it matters

Pitch isn't just a number — it drives real decisions. Steeper roofs shed rain and snow faster, which is why snowy regions favour them, and some coverings only work above a minimum pitch. It affects whether the roof is safe to walk on and how it's built. And it changes the surface area: a steep roof has considerably more slope area than its footprint, so getting the pitch right is essential when estimating materials like tiles, felt or the underlay you need to buy.

Worked with our own calculator

Roof pitch calculator

Given

Rise (cm): 30
Run (cm): 100

Result

Angle (°): 16.699
Slope (%): 30%
Pitch (x-in-12): 3.6

These figures are produced by the calculator below, not typed in by hand — they are recomputed whenever the tool changes.

Run it on your own figures →

Frequently asked questions

How do I measure roof pitch?: Measure the vertical rise over a 12-inch horizontal run; that's the x:12 pitch.
What does a 6:12 roof pitch mean?: The roof rises 6 inches for every 12 inches across, about 26.6°.
How do I convert roof pitch to degrees?: Take the inverse tangent (arctan) of the rise divided by the run.

Articles you may find interesting

All guides →

How-toHow Much Gravel Do I Need?Multiply area by depth for a volume, then convert to weight — gravel is about 1.5 tonnes per cubic metre. Here's the method, depths by job, and how to order.How-toHow Much Mulch Do I Need?Multiply the bed's area by the depth you want. Here's the volume formula, how deep to spread it, bags vs bulk, and the cubic-yard version.How-toHow Much Concrete Do You Need?Concrete is measured by volume: length × width × depth. Here's how to work out cubic metres, add for waste, and choose bags or ready-mix.GuideMaterials for a Retaining Wall — And the Thing That Actually Makes Them Fall OverBlocks, base gravel, drainage stone, geogrid and pipe, counted from the calculator's own output. Then the number nobody puts in a materials list: a saturated backfill pushes about 2.2 times as hard as a drained one.How-toHow Many Tiles Do You Need? (Floor and Wall)Estimate tiles from the area to cover and one tile's size, then add for cuts and waste. Here's the method, with an example and the 10% rule.How-toWhat Size Air Conditioner Do I Need?Around 20 BTU per square foot is the starting rule. Here's how to size a unit from your room's area, adjust for sun and use, and why bigger isn't better.

Sources

Spotted a mistake in this article?