Updated July 18, 2026
How it works
The calculator divides your total rise by the ideal riser height, rounds to the nearest whole number of steps, then back-calculates the exact riser. Total run is (steps minus 1) times tread depth. Stringer length comes from the Pythagorean theorem on the rise and run triangle.
The riser and tread limits above come straight from the IRC stairway section cited below, not a rounded approximation.
Under the IRC, risers cap at 7-3/4 inches and treads run at least 10 inches deep. Those two limits set how steep a residential stair can be, so size your step count to stay inside them.
A worked example
Say the total rise from one finished floor to the next is 36 inches. Aim for a 7 inch riser: 36 divided by 7 is 5.14, which rounds to 5 steps. Divide back and your actual riser is 7.2 inches, comfortably under the 7-3/4 inch ceiling. With a 10 inch tread, the run is 4 spaces (steps minus 1) times 10, or 40 inches. The stringer is the hypotenuse: the square root of 36 squared plus 40 squared is about 53.8 inches, a little under 4.5 ft. Cut your stringer stock longer than that and trim to fit.
What the code requires
The International Residential Code sets the safety limits most jurisdictions follow. Maximum riser height is 7-3/4 inches (R311.7.5.1). Minimum tread depth is 10 inches (R311.7.5.2). Within a single flight, risers and treads have to be uniform: the largest and smallest cannot differ by more than 3/8 inch. That last rule matters more than people expect, because the odd shallow step at the top or bottom is exactly where falls happen. Always confirm against your local amendments before you cut.
Code limits at a glance
| Requirement | IRC limit |
|---|---|
| Max riser height | 7-3/4 in (R311.7.5.1) |
| Min tread depth | 10 in (R311.7.5.2) |
| Riser/tread uniformity | within 3/8 in across a flight |
| Comfortable target riser | about 7 to 7.5 in |
Common mistakes
Forcing a tall riser to save a step is the classic error. It puts the stair over code and makes the climb feel steep. The fix is to add a step and let the riser drop. The other trap is uneven steps where the slab or subfloor was not where you measured, so check your total rise off the finished surfaces, not the rough framing. And give yourself enough run: a stair needs floor space at the bottom, so confirm the total run fits the room before you commit the stringers.
Sources: ICC IRC R311.7.5 (stairways), riser and tread limits.