Calculator
Stair Rise & Run Calculator
Stair rise and run aren't independent choices — building codes set a comfort and safety range for both (commonly 7 to 7.75 inches of rise and 10 to 11 inches of run per step) because a stair outside that range genuinely trips people more, whether it's too steep or unusually shallow. The math starts from total height to climb and available horizontal run, then divides evenly into a whole number of steps within the comfortable range.
This calculator takes your total rise (floor-to-floor height) and target run, solves for step count and individual rise/run, and flags anything outside the standard comfort range. See how to calculate stair rise and run for the underlying 2R+T formula and a worked example.
Calculate your quantity
Number of steps
14 steps
Actual rise per step
7.5 in
- Run per step
- 10 in
- Comfort check (2R+T)
- 25
- Within the standard 24-25 comfort range.
This is an estimate — confirm structural work with a professional.
How this calculation works
Step count = total rise / target individual riser height, rounded to a whole number (this is why total height rarely divides evenly — the calculator adjusts individual riser height slightly so the whole staircase comes out to a consistent, code-compliant rise per step rather than one odd step at the top or bottom). Individual run per step is then checked against the classic comfort formula: 2 x rise + run should land between about 24 and 25 inches — too far outside that range and a stair starts to feel awkward even if each number individually looks fine on paper.
Total run (horizontal footprint) = number of treads x run per step, which matters for space planning since a shallower rise (more comfortable) needs more total horizontal space than a steeper one.
Common mistakes
- Assuming total height divides evenly into a chosen riser height — it almost never does, and the fix is adjusting riser height slightly across all steps, not leaving one mismatched step.
- Ignoring the 2R+T comfort formula and picking rise/run independently, which can produce a stair that's technically within each individual code range but still feels off to walk.
- Not leaving headroom clearance above the stair in the calculation — rise/run sizing doesn't automatically guarantee adequate headroom on a stacked floor plan.
- Building interior stairs to exterior-stair codes or vice versa — the two sometimes have different allowed ranges depending on local code.
- Forgetting the top or bottom step's relationship to finished flooring — a stringer cut for a bare subfloor needs adjusting once flooring thickness is added, or the top step ends up a different height than the rest.
- Not checking handrail and guardrail requirements alongside rise/run — most codes require a graspable handrail above a certain number of risers, which is a separate but related requirement easy to overlook while focused purely on the rise/run math.
Shopping summary
This is a structural layout calculation, not a shopping list — use the resulting step count and per-step rise/run to plan stringers and confirm against your local building code before cutting stringers; this is an estimate — confirm structural work with a professional.
Worked example: a deck with 30 inches of total rise to grade, targeting a 7-inch riser, gives 30/7 ≈ 4.3 steps — round to 4 steps at 30/4 = 7.5 inches each, still within most codes' allowed riser range. Solving for run at the 2R+T ≈ 25 target: run = 25 - 2(7.5) = 10 inches per tread, for a total horizontal footprint of 4 x 10 = 40 inches from the deck edge to grade.
FAQ
Why doesn't my total height divide evenly into 7-inch steps?
Total rise is essentially never an exact multiple of a chosen riser height — the standard fix is to adjust the riser height slightly (while staying within code's allowed range) so all steps come out equal, rather than building one odd-height step.
What is the 2R+T formula?
It's a long-used stair-comfort guideline stating that twice the riser height plus the tread run should total roughly 24-25 inches — stairs built well outside that range tend to feel unusually steep or unusually shallow even when each individual number is within code minimums.
Do exterior deck stairs use the same rise/run limits as interior stairs?
Often similar but not always identical — some jurisdictions allow slightly different tolerances for exterior stairs, and outdoor stairs also need to account for water drainage off the tread surface, which isn't a factor for an interior staircase.
How much does riser height variance actually matter for safety?
More than intuition suggests — most codes limit the difference between the tallest and shortest riser in a single flight to a small fraction of an inch (commonly around 3/8 inch), because people unconsciously expect each step to feel the same, and even a small inconsistency is a well-documented, disproportionately common cause of trips.