For roof slopes expressed as x in 12 rise in run the roof pitch multiplier is determined by finding the square root of rise run 1.
Formula roof pitch multiplier.
The calculator above can handle much of this math.
Here are the equations you may use to solve for the length of the slope and the rafter.
Measure the rise of your roof.
Step 1 multiply 20 and 40 which equals 800.
Let s say it is equal to 1 5 m.
Rafter rise run 1 5 6 2 25 36 38 25rafter 38 25 6 18 m.
Now you re ready to price out the materials.
Now solving for c in the equation above gives.
Since pitch is the rise over a 12 inch run divide the run by 12 to get the multiplier in this case 120 12 10.
A roof pitch multiplier also called a roof pitch factor is a number that is multiplied by the area covered by a sloped roof to produce the area of the actual surface of the roof.
Pitch rise run 1 5 6 25.
48 10 4 8.
Step 3 multiply step 1 and step 2 i e.
Next multiply the footprint of the roof by the multiplier below for your roof pitch to find the overall roof area.
For example a 4 12 pitch roof that is 100 square feet.
Image 1 12 to 12 12 roof pitch 7 12 pitch.
You can also calculate roof pitch even without using a roof slope calculator.
The formula for the roof pitch multiplier comes from the famous pythagorean theorem.
Take your area result and multiply it by the pitch multiplier or slope correction factor found in the table above to arrive at the roof s surface area.
If your roof is flat or has no more than a 3 in 12 pitch you can calculate its total square footage by simply multiplying the length by the width.
Steep roofs measure your house at ground level then add in the roof s overhang for greater accuracy.
800 multiplied by 1 16.
Roof pitch degree table.
Step 2 find the value of 7 12 from the roof slope multiplier table which is 1 16.
100 1 054 105 4ft2.
Use the following formula which also describes a right triangle.
Where a is the rise of the roof b is the run of the roof and c is the rafter hypotenuse of the triangle with side lengths a and b.
Now divide the rise by the multiplier to get the pitch eg.
Rafter rise run this formula is from the pythagorean theorem.
If the home measures 20 x 40 and has a 7 12 roof then to calculate the slope of the roof follow these steps.
Calculate the rafter length substituting these values into the following formula.
