Stair Calculator
A stair calculator works out your staircase layout from the total height (total rise). It divides the total rise into equal steps of a comfortable height (about 7.5 inches), then gives the number of steps, the exact rise and run per step, and the stringer length. Enter your total rise below to get the full layout.
Enter your total rise (floor-to-floor height) to see the layout.
Estimate only. Confirm against your local building code: stairs, framing, rebar, roofing and retaining walls are structural and code-dependent. This site does not provide engineering judgment.
How Do You Calculate Stairs?
To calculate stairs, start with the total rise (the vertical height from the lower floor to the upper floor). Divide it by a comfortable step height of about 7.5 inches and round to the nearest whole number to get the number of steps. Then divide the total rise by that step count for the exact rise per step. For a 108 inch total rise, that is 14 steps at about 7.71 inches each. The calculator also gives the run and stringer length.
What Is a Comfortable Stair Rise and Run?
A comfortable and code-typical stair has a rise (step height) between 7 and 7.75 inches and a run (step depth) between 10 and 11 inches. Building codes set maximum rise and minimum run for safety, and steps must be uniform: every rise within about 3/8 inch of the others. The calculator targets these comfortable values and keeps all steps equal, but always confirm against your local building code.
How Do You Calculate a Stair Stringer?
A stair stringer is the diagonal board that supports the steps, and its length comes from the total rise and total run using the Pythagorean theorem: stringer length is the square root of (total rise squared plus total run squared). For a 108 inch rise and 140 inch run, the stringer is about 177 inches along the diagonal. The calculator computes this so you can buy stringer stock of the right length.
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Frequently asked questions
- How do I calculate the number of stairs?
- Divide the total rise (floor-to-floor height) by about 7.5 inches and round to a whole number. A 108 inch rise gives 14 steps at about 7.71 inches each.
- What is a comfortable stair rise?
- A rise of 7 to 7.75 inches per step with a run of 10 to 11 inches is comfortable and code-typical. Steps must be uniform within about 3/8 inch.
- How do I calculate stringer length?
- Use the Pythagorean theorem: the square root of (total rise squared plus total run squared). A 108 by 140 inch staircase needs a stringer about 177 inches long.