What Is a Pitch Multiplier (And What Does It Have to Do With Your Roof)

A pitch multiplier is a number that allows you to find the total surface area of your roof. Simply multiplying this number by the area covered by a sloping roof to obtain the total surface area of the roof itself. Considering a roof can be challenging to measure by itself, this multiplier will greatly assist! 

The formula for the pitch multiplier actually comes from the famous Pythagorean Theorem which states 

a² + b²⁼ c²      The  “a” is the Rise of the roof, the “b” is the Run of the roof, and the “c” is the Rafter or hypotenuse. After solving this equation, it resolves to this:

Pitch Multiplier =   c  ⁄  b

The following chart is an excellent guide to roof pitch, angle, and the corresponding pitch multiplier:

• 1 ⁄ 12; 4.76°; 1.0035
• 2 ⁄ 12; 9.46°; 1.01
• 3 ⁄  12; 14.04°; 1.0308
• 4 ⁄ 12; 18.43°; 1.05
• 5 ⁄ 12; 22.62°; 1.08
• 6 ⁄ 12; 26.57°; 1.12
• 7 ⁄ 12; 30.26°; 1.16
• 8 ⁄ 12; 33.69°; 1.20
• 9 ⁄ 12; 36.37°; 1.25
• 10 ⁄ 12; 39.81°; 1.30
• 11 ⁄ 12; 42.51°; 1.36
• 12 ⁄ 12; 45.00°; 1.41

The pitch is explained like this: if for every 12 inches, the roof rises by 5 inches, then the slope will be 5/12

How can I use this information to benefit me as a homeowner? You can use this simple method to make sure your roofing contractor is honest and reliable in their calculations. 

If a home measures 20 x 40, and has a 7/12 roof, then calculate the slope of the roof this way:

1. Multiply 20 x 40 which equals 800
2. Find the value of 7/12 from the table above. That multiplier number is 1.16
3. Multiply Step 1 and Step 2 (800 multiplied by 1.16)
4. The value arrived at 928 reflecting the square feet of the roof. 

Through the help of the above table and example, your roof can be measured. This can be helpful when designing an addition, installing skylights, or cutting new rake boards. 

If you desire to keep the memory of math back in the high school memory block, then contact us for assistance! We are Prominent Construction of Minneapolis. We have the knowledge and experience in figuring out pitch, slope, and multiplier information. 

You can keep your trust in us and know we will do what is best for you, your home, and your budget. Place your trust in a company that has your back! Give us a call and we can discuss all things in residential roofing and commercial roofing and how we can best assist you. We look forward to hearing from you!