Rafter rise run this formula is from the pythagorean theorem.
Formula roof pitch multiplier.
Step 1 multiply 20 and 40 which equals 800.
Steep roofs measure your house at ground level then add in the roof s overhang for greater accuracy.
48 10 4 8.
Here are the equations you may use to solve for the length of the slope and the rafter.
Let s say it is equal to 1 5 m.
Use the following formula which also describes a right triangle.
Now you re ready to price out the materials.
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.
For example a 4 12 pitch roof that is 100 square feet.
Calculate the roof pitch as the proportion of rise and run.
Step 2 find the value of 7 12 from the roof slope multiplier table which is 1 16.
Rafter rise run 1 5 6 2 25 36 38 25rafter 38 25 6 18 m.
Use our roof pitch calculator to find the pitch of your roof.
You can also calculate roof pitch even without using a roof slope calculator.
The calculator above can handle much of this math.
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.
Calculate the rafter length substituting these values into the following formula.
Step 3 multiply step 1 and step 2 i e.
Pitch rise run 1 5 6 25.
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.
Image 1 12 to 12 12 roof pitch 7 12 pitch.
Measure the rise of your roof.
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.
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.
Roof pitch degree table.
Now solving for c in the equation above gives.
Now divide the rise by the multiplier to get the pitch eg.
The pitch of this roof is 4 8 12.
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.
If the home measures 20 x 40 and has a 7 12 roof then to calculate the slope of the roof follow these steps.
800 multiplied by 1 16.