This works out how many steps a staircase needs and their exact riser height, always splitting the total rise evenly across every step, plus the stringer length if you know the total horizontal run.
How it works
Steps and riser height
steps = ⌈total rise ÷ target riser⌉ · actual riser = total rise ÷ steps
The stringer length, if a total run is given, follows the Pythagorean theorem: √(rise² + run²).
Why every step is always the same height
A staircase with one riser noticeably taller or shorter than the rest is a well-documented, common cause of missteps — human gait expects a consistent rhythm, and the one odd step is exactly where people trip. This calculator always divides the total rise evenly across every step, rather than using a target height for most steps and dumping a leftover remainder onto the last one.
This is geometry, not a code compliance check
Maximum riser height, minimum tread depth and other stair dimensions are set by local building codes, which vary by jurisdiction. A commonly cited comfortable range is roughly 7–7.75 inch risers, but “commonly cited” is not the same as “legally required where you are.” This calculator computes the geometry correctly for whatever riser height you enter; whether that height is permitted, and by which code, is a question for a local building inspector.
How to use this calculator
- Enter the total floor-to-floor rise.
- Enter a target riser height — check your local code for what’s permitted.
- Optionally add the total horizontal run to also get the stringer length.
Frequently asked questions
Why does the actual riser height differ from my target?
Because the total rise rarely divides evenly by the target height — the calculator rounds the step count up to a whole number, then splits the total rise evenly across that many steps, which shifts the actual riser height slightly from the target you entered.
What is a stringer, and why does its length matter?
The stringer is the diagonal structural piece the steps attach to — its length is the actual board length needed to cut, which is always longer than either the total rise or the total run alone, following directly from the Pythagorean relationship between them.
Does this calculator check my local building code?
No — it computes the geometry correctly for whatever numbers you enter. Whether a given riser height or tread depth is legally permitted is set by your local jurisdiction’s building code, which this calculator does not know and cannot check.
Why is uneven riser height actually dangerous, not just uncomfortable?
Because people’s stepping rhythm on a staircase adapts to the first few steps and then continues largely on muscle memory — a step that breaks that established rhythm is disproportionately likely to catch a foot, which is exactly why building codes commonly set a maximum allowed variation between risers.
What if my total rise already divides evenly by my target riser height?
Then no adjustment happens at all — the actual riser height comes out exactly equal to your target, since there is no remainder left to redistribute.
