How to Calculate Your Roof’s Pitch

The pitch of your roof is a measure of how steep it is, and it’s important for more than just appearance. Roof pitch (sometimes more correctly called slope) determines how easily water runs off a roof during a storm and what type of roofing materials the roof can support. 

Luckily, it’s pretty simple to calculate your roof pitch yourself. All you need is a tape measure, a spirit level, a pen, a piece of paper, and our calculator. Keep reading, and we’ll teach you how to use these tools to calculate your roof’s pitch. We’ll also explain what your roof’s pitch means for your roof and your future home improvement projects.

Roof pitch glossary

To better understand the rest of this guide, you should first get familiar with these terms:

Run

Run is the measurement of the horizontal distance between the leftmost and rightmost points of a right triangle. In roofing, it’s standard to compare 12 inches of run against a roof’s vertical rise. 

Rise

Rise is a measurement of the vertical distance between the lowest and highest points of a right triangle. In roofing, the rise is usually defined as how high a roof climbs upward over 12 inches of horizontal run. 

Span

Span: A roof’s span is the entire horizontal distance between one edge of the roof and the other. Because it’s also a measurement of horizontal space, span is similar to run, though run is usually just a small portion of a roof’s span. 

Slope

Slope is a measurement of how steep a triangle is, and in roofing, it’s usually written out as a rise/run ratio in inches. A triangle with a 12-inch horizontal run and a four-inch vertical rise will have a 4/12 (sometimes written as 4:12) slope, meaning it rises four inches for every 12 inches it runs. In the modern roofing industry, the slope is often called “pitch” instead. 

Pitch

While pitch historically referred to the relationship between a roof’s entire span and its entire rise (instead of just a section of the roof), it is now used synonymously with “slope” in the roofing industry. In fact, slope is more commonly called pitch by many roofers these days. Because of this, we’ll simply refer to “slope” as “pitch” throughout this article. 

Two methods for calculating your roof’s pitch

You only need a few everyday tools to take measurements and find your roof’s pitch. 

What you need

You can’t accurately determine your roof’s pitch by just eyeballing it, and accuracy is key when working on your roof. Luckily, you just need a few tools to get precise measurements:

• A tall ladder
• A foot-long spirit level
• A tape measure or a ruler

Method 1: Calculate your roof’s pitch from atop your roof

Measuring your roof’s pitch is as simple as finding its rise and run. Remember, rise is vertical distance, and run is horizontal. For every foot that your roof extends horizontally, it rises "x" amount of inches.

To determine the "x," use this simple measuring technique:

• Step 1: Carefully access your roof using your ladder.
• Step 2: Measure 1 foot up from the base of the roof using your measuring tape. This will give you the horizontal run.
• Step 3: Place one end of your level at the 1-foot mark, but make it create an "L" shape away from your roof by suspending the opposite end in the air.
• Step 4: Once the bubble of air in the level’s horizontal vial is in the middle, measure from the bottom of the level to the top of the roof. The distance you measure will be your roof’s vertical rise.
• Step 5: Enter your measurements into our calculator to get your results. 

For example, if what you measured for the rise is six inches, then the pitch of the roof is 6/12. This means that for every 12 inches of horizontal length of the roof, the roof rises six inches. 

Roofs with steeper pitches will have a higher rise number, say 10/12. Roof pitches can also be much lower, and they can be as low as 2/12 for roofs with asphalt shingles or even lower for metal roofs or gambrel-style homes with roofs that have many differently-pitched sections. 

If your entire roof is simple and uniformly shaped (it doesn’t feature differently-pitched eaves, overhangs, or dormers), you just have to take pitch measurements once, and you can gather them just about anywhere on your roof.

If, however, your roof has various features that each have its own pitch, you’ll need to take measurements of every roof area and calculate each one separately to get a complete assessment of your roof’s various pitches.

Method 2: Calculate your roof’s pitch from inside your attic

The underside of your roof will have the same pitch as the top, so you can take your pitch measurements along a rafter length in your attic. Image source: Reddit

If you cannot access your roof or don’t feel comfortable doing so, you can safely measure your roof pitch using a rafter or a roof truss within your attic.

• Step 1: Access your attic and find a roof rafter or truss. It will be a wooden beam that runs diagonally along the ceiling of your attic. 
• Step 2: Measure 12 inches of horizontal run up the beam from your attic floor.
• Step 3: To find the vertical rise of your roof, start at the 12-inch mark you measured on your truss and simply measure vertically downward to the attic floor.
• Step 4: Put your measurements into our calculator to find your roof’s pitch.

Say the distance from the floor of your attic to the 12-inch mark on your rafter is 6 inches. This would mean your roof pitch is 6/12.

As before, if your roof has multiple structural features with different pitches, you’ll also need to separately find the pitches for each one by repeating this process.

Common roof pitches

Roofs come in all shapes and pitches, though some pitches are more common than others. 

The pitch of a roof can have a significant impact on its structural integrity, its ability to support different roofing materials, and its ability to quickly shed water, ice, and other debris. Depending on what type of roof you have, it will have a different pitch.

Flat roofs or low pitch/low slope roofs will typically have a lower ratio and fraction, usually from 1/12-2/12.

The most common pitch for standard gable roofs is between 4/12 and 8/12. This pitch provides enough slope for adequate runoff while also providing the necessary stability for roofing materials like shingles and tiles. 

On exceptionally steep roofs, you sometimes see pitches of up to 18/12 or higher. These roofs will shed snow buildup and drain water quicker than standard roofs. 

The best roof pitch for your region

If you live in a region with frequent rain or snowfall, then you’ll want a relatively steep roof pitch to promote healthy runoff. This will prevent water from pooling on your roof (as long as you keep your gutters in good shape) and ice from weighing on your rafters. Generally, a roof pitch steeper than 6/12 will serve you well in areas where inclement weather is common. 

If you live in an arid area, though, you could very well get a lower roof pitch. Most residential roofs don’t feature pitches more gradual than 4/12 because they can have runoff issues. Still, if your region never sees snow and rarely gets any rainfall, you could get away with a flatter roof if you get the right roofing materials. 

Materials that work best with different roof pitches

Roofing materials for flat roofs

If your home has a flat roof, then your options for roofing materials are fairly limited. Flat roofs don’t drain water very effectively, so shingles and tiles are more likely to leak on flat roofs. Additionally, flat roofs typically can’t support as much weight as roofs with steeper pitches, so heavy roofing materials are usually out of the question. 

For these reasons, there are only two roofing materials that work well with flat roofs:

• Rubber roofs
• Lightweight standing seam metal roofs

Roofing materials for pitched roofs

If your roof has a steeper pitch, you have a lot more options for what you can cover it with. The table below lists the minimum required pitch for various roofing materials. 

Be aware, though, that minimum roof pitch can vary depending on the manufacturer who crafted your roofing materials, and some materials require additional roofing reinforcement. This means you should talk with a roofer about which materials are actually right for your roof. 

Minimum roof pitch for different roofing materials

Calculating your roof’s pitch

Now that you know how to find the pitch of your roof, you’re ready to take the next step in your roofing project. If you want to repitch your roof because its current pitch doesn’t meet your needs, that is an option, though roof repitching is a costly and difficult process.

Frequently asked questions

What is a roof’s pitch?

“Roof pitch” is a term that describes how steep a roof is. It’s usually measured by comparing 12 inches of a roof’s horizontal “run” to how much it “rises” across that same distance. For example, if a roof rises four inches for every 12 inches it runs horizontally, it has a 4/12 (or 4:12) pitch. 

This wasn’t always what roof pitch meant, though. Pitch used to be a measure—expressed as a simple fraction—that denoted how much a roof rose to its highest point across its entire span. For example, a roof that rose four feet across a 24-foot span would have a 1/6 pitch. 

What is a roof’s slope?

Slope is technically the more correct term for what is often called “pitch” in modern roofing.  It’s a measure of how steep a roof is, calculated by comparing how much a roof rises upward across 12 inches of horizontal run. A roof that rises six inches across 12 inches of run has a slope of 6/12 (sometimes written as 6:12). 

What is the standard pitch for a roof?

Roof pitches between 4/12 and 8/12 are most common, though roofs come in an immense variety of shapes and sizes. Depending on what roofing materials you want and what you want your roof to look like, you can get a roof with a steeper or a more gradual pitch.

Can you change a roof’s pitch?

Yes, you can change the pitch of your roof, but it requires significant, costly changes to the structure of your roof. In some cases, it can cost well over $20,000 to reframe your home’s roof. However, this might sometimes be necessary if your old roof has collapsed or you want your roof to support a different roofing material. 

What roof pitch is walkable?

Walking on any roof—even a flat roof—comes with significant risk and is best left to professionals. However, most people can safely walk on roofs with pitches below 6/12. If your roof’s pitch is 6/12 or less, you can probably walk on it to make DIY repairs, clear debris, or hang holiday lights. Just be careful!