What roof pitch means
Pitch is how steep a roof is, written as the rise in inches for every 12 inches of horizontal run. A 6/12 roof rises 6 in over 12 in, which is an angle of about 26.6°. Outside North America, roof slope is more often given in degrees.
| Pitch | Angle | Typical description |
|---|---|---|
| 2/12 to 3/12 | 9.5° to 14° | Low slope |
| 4/12 to 6/12 | 18° to 27° | Common on houses |
| 7/12 to 9/12 | 30° to 37° | Steep |
| 12/12 | 45° | Very steep |
Shingle manufacturers set a minimum slope for their products. Many asphalt shingles require at least 2/12 with special underlayment, and 4/12 for standard installation. Read the wrapper and follow its rules.
How to measure pitch
The safest way is from inside the attic. Hold a level horizontally against the underside of a rafter, mark 12 inches along the level, and measure straight up from that mark to the rafter. That number is the rise. You can also use house plans or an angle-measuring app from a ladder at the eave. Avoid walking on the roof to measure it.
Why pitch changes the amount of roofing
A sloped roof is longer than the flat area beneath it. The steeper the slope, the more surface there is to cover. The multiplier, or pitch factor, is √(1 + (rise ÷ 12)²). At 6/12 it is 1.118, so a 1,500 sq ft footprint has about 1,677 sq ft of roof surface.
Squares
A roofing square is 100 sq ft of roof surface. A 1,677 sq ft roof is 16.8 squares before waste. Contractors usually add 10 to 15 percent for cutting, starter rows and ridges, more for roofs with many valleys and dormers.
Bundles
Standard asphalt shingles are packed so that three bundles cover one square. Heavier laminated or designer shingles may need four or five bundles per square. A bundle of standard shingles typically weighs somewhere around 60 to 80 lb, so plan how the material will get onto the roof.
The other materials
- Underlayment covers the whole deck. Roll coverage varies by product.
- Starter strip runs along every eave and rake edge.
- Ridge cap covers ridges and hips, sold by linear coverage.
- Drip edge, flashing and nails complete the job.
Get the squares and bundles for your house from the roofing calculator.
Frequently asked questions
What is the most common roof pitch?
Many houses in North America have roofs between 4/12 and 9/12, with 6/12 being very common.
How many square feet does a bundle of shingles cover?
A bundle of standard asphalt shingles covers about 33.3 square feet, a third of a square.
Does a hip roof need more shingles than a gable roof?
For the same pitch and footprint, the surface area is similar, but hips need more cutting and ridge cap, so allow more waste.
Do the math for your own project.
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