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.
Formula roof pitch multiplier.
Here are the equations you may use to solve for the length of the slope and the rafter.
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.
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.
The pitch of this roof is 4 8 12.
Rafter rise run this formula is from the pythagorean theorem.
And for a roof with a slope of 6 12 that number 1 118 is your roof slope multiplier.
Next multiply the footprint of the roof by the multiplier below for your roof pitch to find the overall roof area.
The calculator above can handle much of this math.
48 10 4 8.
100 1 054 105 4ft2.
Now divide the rise by the multiplier to get the pitch eg.
Step 1 multiply 20 and 40 which equals 800.
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.
Step 2 find the value of 7 12 from the roof slope multiplier table which is 1 16.
Use our roof pitch calculator to find the pitch of your roof.
Take the area of the roof s footprint say it s 5 000 square feet and multiply 5 000 by 1 118.
The formula for the roof pitch multiplier comes from the famous pythagorean theorem.
Measure the rise of your roof.
Rafter rise run 1 5 6 2 25 36 38 25rafter 38 25 6 18 m.
Use the following formula which also describes a right triangle.
Step 3 multiply step 1 and step 2 i e.
Let s say it is equal to 1 5 m.
Pitch rise run 1 5 6 25.
Steep roofs measure your house at ground level then add in the roof s overhang for greater accuracy.
For example a 4 12 pitch roof that is 100 square feet.
Image 1 12 to 12 12 roof pitch 7 12 pitch.
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.
That gives you 5 590 square feet which is the actual area of the surface of the roof.
You can also calculate roof pitch even without using a roof slope calculator.
Calculate the roof pitch as the proportion of rise and run.
800 multiplied by 1 16.
Roof pitch degree table.
So the actual roof surface if it were laid down flat on the ground would be 1 118 times larger than the footprint of the roof.
