# what's the formula for building stairs?

• posted on March 31, 2005, 4:30 pm
I saw a formula to figure out the stringer, risers, and threads somewhere. And lost it.
Now I need it, tried Google and must not asked the right questions.
Feel free to email me directly.
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My family coat of arms ties at the back.....is that normal?
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• posted on March 31, 2005, 5:22 pm

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• posted on March 31, 2005, 7:13 pm
If you are looking for the riser / tread ratio, an old copy of Architectural Graphic Standards would be a help. The 5th Edition, pg 222 has a nice comparison of several formulae.
I use 2R+T = 25 (example: R=7" & T= 11" : 2 @ 7 + 1 @ 11 = 25)
TB
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• posted on April 1, 2005, 3:15 am
snipped-for-privacy@bellsouth.net wrote:

Another one is 1 riser plus tread = 17". Been too long and I don't recall the figure: there is a limit on riser height (or tread depth to put it the other way) that will pass code.
Harry K
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• posted on April 1, 2005, 4:26 pm
I have a 6th edition and I couldn't find that section. I assume it's in the carpentry chapter. What subject matter is nearby in the 5th edition? thanks Bill

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• posted on April 2, 2005, 12:35 am

Standards are great, that's why we have so many of them. But if you're putting a stairway in a normal sized house, the constraints of the available space will matter more than any formula. You divide the floor-to-floor height evenly into the smallest number that yields less than 8" of rise per step. Then you figure out how to cram that into the available run, figuring no less than 10" and no more than 11.25" of tread, and no more than 1" of overhang for the bullnose (if any).
And remember that you need 6'8" of overhead, measured from the front of the treads.
California's rules are here: http://www.dir.ca.gov/Title8/3231.html