How to Calculate Stair Stringer Length

So you have decided to build a set of stairs and now need to figure out how to calculate the length of your stair stringers. Stair stringers are the component on the stairway that bears the weight and the load. There are a few easy things you can do to calculate this length.  All you need is a measuring tape and the outline for your stairway to begin.

Length of Stringers in General Terms

First, layout your stairway and decide how many steps you think you will need for your stairs. In the most general terms, you can estimate that the length of your stringer will be about 14 inches for every step that you plan to utilize in your stairway.

Using a Little More Math

If you would like a little more precise calculation for your stair stringers, then follow the below calculations. First, take the measurements of the following:

  1. The Riser
  2. The Stair Tread

Multiple 1 x 1 and 2 x 2 (the riser length x itself and the stair tread length x itself). Then take the result from each of your calculations and add the two resulting numbers together. Once you have this number, find the square root (you will find this function on your calculator). Take the square root number and multiply it by the number of steps you will use in your stairway. Voila - you now have a pretty accurate number for the length of your stair stringer.