Things You'll Need
Pen or Pencil
There are three main components in a standard staircase: stringers, risers and treads. The stringer is the backbone of the structure. Stringers are the diagonally placed boards, anchored at the top (the header) and the bottom (the footer) of the staircase. They support the treads (the surface you step on) and the risers (the backing that makes sure your foot does not go between each step). Measuring a stringer is an exact process that must adhere to both local building code and common sense for safety.
Measure the total rise, or overall height, that your staircase will be covering. This is the distance from the ground to the point of termination of your staircase.
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Determine your desired step rise, the height of each step. Between 7 and 7.5 inches is standard, anything greater will result in a steep staircase and can be dangerous. Anything less will require more lumber as it will increase the number of steps necessary to cover the given distance.
Determine your desired run. This dictates the width of each step. A wider step is safer and the optimal run is no less than 10 inches.
With these three measurements, you can calculate your stringer's measurements. The first calculation finds the actual number of steps. Let's say the overall height your stairs will be covering is 61 inches. Using the standard 7-inch rise, divide 61 by 7 to get 8.71. Rounding to the nearest whole, you find that your staircase will have nine steps.
Determine the actual rise of your stringer. Divide 61 inches by nine steps to get 6.78 inches per step. Your stringer will have nine steps each with a rise of 6.78 inches.
Use this information to determine the total run, or horizontal area, your staircase will cover as it climbs. Multiply the number of steps, nine in our example, by the run of each step, 10 inches as per standard, to get 90 inches.
Using these simple calculations, you find that your stringer will be 90 inches long, with a total rise of 61 inches, a step rise of 6.78 inches and a step run of 10 inches.
A wider staircase is a safer staircase, but keep in mind that stringers should not be more than 16 inches apart to provide continual stability. If your staircase is going to be wider than 20 inches, you will need more than two stringers. In this example, the staircase is 36 inches wide, so you will need 3 stringers to prevent sagging or breakage in the middle of each step.
You will be cutting your stringers out of a 2-by-12 board that is unlikely to be longer than 16 feet. This means that you will be unable to get more than 14 steps per stringer.
Be sure to use pressure-treated lumber when building outside.
Not using the standards recommended could result in an unsafe or unstable staircase that may cause injury or death.
Be sure to check local building codes to make sure your project meets safety standards or it could be ordered torn down.
The methods provided in this article are best suited to the construction of outdoor stairs.