Roof Pitch Calculator: Figure Rise per Foot

This roof pitch calculator works out the slope of your roof as a ratio of rise over run (inches of rise per 12 inches of run) and also gives you the angle in degrees and the slope percentage. You enter the vertical rise and the horizontal run (or the total span if you only have that), and you get back the pitch ratio, the angle, and the slope percentage.

Formula

The roof pitch is the ratio of vertical rise to horizontal run, expressed as inches of rise per 12 inches of run. The formula is:

Pitch (in/12) = (Rise ÷ Run) × 12

Where:

• Rise = vertical distance the roof climbs (in inches)
• Run = horizontal distance over which that rise occurs (in inches)
• Pitch = the standard roof pitch notation, e.g., 6/12

The angle in degrees is found with the arctangent: Angle = atan(Rise ÷ Run), and the slope percentage is simply Rise ÷ Run × 100.

Worked Example

Using the default values from the calculator (rise = 6 inches, run = 12 inches):

1. Pitch = (6 ÷ 12) × 12 = 0.5 × 12 = 6 in/12in (a 6/12 pitch)
2. Angle = atan(6 ÷ 12) = atan(0.5) ≈ 26.57°
3. Slope = (6 ÷ 12) × 100 = 50%

So a roof that rises 6 inches for every 12 inches of horizontal run is a 6/12 pitch, which is a common, moderately sloped roof.

How to Measure Your Roof’s Rise and Run

To use the calculator you need two measurements. The easiest way is to work from inside the attic:

• Place a level horizontally against a rafter, and measure 12 inches along the level from the rafter’s bottom edge.
• From that point, measure straight down to the rafter’s bottom edge – that vertical distance is the rise for a 12‑inch run.
• If you measure a different run (like 24 inches), just divide the rise by that run and multiply by 12.

Alternatively, if you know the total span (the horizontal width of the building) and the total rise (from the top of the wall to the ridge), you can use half the span as the run. For example, a building with a 24‑foot span and a 6‑foot total rise has a run of 12 feet and a rise of 6 feet – that’s a 6/12 pitch.

Why Roof Pitch Matters

Pitch affects more than just looks. It determines:

• Water shedding: Steeper pitches shed rain and snow faster, reducing the risk of leaks. Low slopes (below 2/12) need special waterproofing.
• Material choices: Asphalt shingles generally require a minimum pitch of 2/12 (or 4/12 for standard shingles). Clay tiles and slate need steeper pitches, often 4/12 or more.
• Attic space: Steeper roofs create taller attics, which can be finished into living space.
• Wind resistance: Very steep roofs catch more wind, while very low slopes can be more prone to uplift in high winds.
• Cost: Steeper roofs use more material and are more dangerous to work on, so they cost more to build and repair.

Common Mistakes and Misconceptions

One common mix-up is confusing “pitch� with “slope percentage.� A 6/12 roof is not a 6% slope – it’s a 50% slope. The pitch ratio is always rise over 12 inches of run, while percentage is rise over run times 100. Another mistake is using the total span instead of the run. Remember: the run is only half the span for a symmetrical gable roof.

People also often measure the rise from the top of the wall to the ridge, but forget that the run is measured horizontally, not along the rafter. If you measure along the rafter, you’re measuring the hypotenuse, not the run. Always use a level to get a true horizontal distance.

Finally, don’t use the calculator for a single‑sloped (shed) roof with a different run than half‑span – just enter the actual run you have.

Limits of the Formula

The pitch formula assumes a straight, uniform slope. It doesn’t account for:

• Curved or gambrel roofs, where the slope changes partway up.
• Irregular rafter spacing or sagging.
• Dormers, valleys, or other interruptions that make the actual roof surface more complex.

For those, you’d need to measure each section separately. The calculator gives you the nominal pitch, which is what contractors use for ordering materials and estimating, but it’s not a substitute for a professional measurement if you’re planning a re‑roof.

Safety and Accuracy Tips

When measuring a roof, safety comes first:

• Never climb onto a roof without proper fall protection – a harness, anchor points, and a helper.
• Measure from inside the attic whenever possible to avoid roof work entirely.
• Use a sturdy ladder and have someone hold it if you must go up.
• Wear shoes with good grip and avoid wet or icy conditions.
• For accuracy, measure at several points along the roof – rafters can vary slightly.

If you’re unsure about the measurements, consult a professional roofer. A small error in pitch can lead to incorrect material orders or inadequate drainage.

Frequently Asked Questions

What does “6/12 roof pitch� mean?

It means the roof rises 6 inches for every 12 inches of horizontal run. It’s a moderate slope that works with most roofing materials and is common in many residential areas.

How do I convert roof pitch to degrees?

Use the arctangent: angle = atan(rise ÷ run). For a 6/12 pitch, that’s atan(0.5) ≈ 26.57 degrees. You can also use the calculator above – it gives the angle automatically.

What is the minimum pitch for asphalt shingles?

Most shingle manufacturers require a minimum pitch of 2/12 (about 9.5 degrees) for their standard product, but many recommend 4/12 (about 18.4 degrees) for best performance. Below 2/12, you need a special low‑slope roofing system like rolled roofing or a membrane.

Can I use this calculator for a shed roof?

Yes, as long as you enter the actual rise and run of the shed roof. A shed roof is a single slope, so the run is the horizontal distance from one wall to the other, not half a span.

Is roof pitch the same as slope percentage?

No. Pitch is rise per 12 inches of run, while slope percentage is rise per run times 100. A 6/12 pitch equals a 50% slope. The calculator shows both, so you can see the difference.

What if my roof has a 12/12 pitch – is that steep?

Yes, a 12/12 pitch means the roof rises 12 inches for every 12 inches of run, which is a 45‑degree angle. That’s quite steep and may require special safety equipment for walking on it, and it will use more material than a lower pitch.

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in rise | Rise (vertical) | in | 6 | 0
in run | Run (horizontal) | in | 12 | 0
out pitch | Pitch (rise per 12 in) | in/12in | rise / run * 12 | 2
out angle | Angle | degrees | atand(rise / run) | 2
out percent | Slope | % | rise / run * 100 | 2