Expert: Dan Griffin - 10/12/2009

Question
Hello,
I an trying to figure out how to calculate the rise and runs of a stair where I have the angle and length of the stairs.

I have alot of experience in framing and remodel construction so I can grasp concepts easily. I just dont know the formula.

Many thanks!

William

Answer
William,  here are a few facts about stairs:
There are several formulae for a comfortable stair
1.  Rise + run = 17-18"
2,  Ruse + run + rise = 25-26"

A rise of 7 with tread of 11 is quite comfortable.

Measure the distance from finish floor top to finish floor bottom.
Let's assume it is 108"
Divide by 7.which will give you 15.4285
This would suggest 15 rises.
Divide the 108 by 15 = 7.2" per riser (just shy of 7 1/4")
A tread from 10 to 11" will work well.
Layout one stringer with a framing square using 7.2 on the tongue and 11 on the blade.
Once you have worked out the top and bottom fastening and layout details, go ahead and cut one stringer, use as a template for the other two.

Code issues about stairs:
No risers over 7 1/2"
The noses of the stairs should all line up, no variation in riser heights greater than 1/4".

I hope this answers your question.