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.
The formula
steps = round(totalRise / targetRise); actualRise = totalRise / steps; comfort = 2×actualRise + targetRun
- steps = round(...)
- Rounded to the NEAREST whole step, not up or down — targeting a 7 in riser on a run that divides out to 6.6 steps rounds to 7 steps, adjusting actual riser height down slightly, while a run at 6.4 rounds to 6 steps and adjusts it up.
- actualRise = totalRise / steps
- The riser height EVERY step in the flight actually gets, recomputed from the rounded step count — this is why the number reported here rarely matches the target rise entered exactly, and is the figure to build to, not the target.
- comfort = 2×actualRise + targetRun
- Uses the RECOMPUTED actual rise, not the original target rise — so this check reflects the real step geometry after rounding, and can flag a stair as outside the comfort range even when the target inputs alone looked reasonable.
Where these numbers come from
- 2R + T between 24 and 25
- Trade convention (the classic stair-comfort rule), applied here as a fixed pass/fail band rather than a code citation — check your local code separately, since some jurisdictions specify riser and tread minimums and maximums directly rather than through this ratio.
- steps rounded to the nearest whole number, not ceiling'd
- The function's rounding choice is worth spelling out on its own: rounding UP would always shrink the riser below target and rounding DOWN would always grow it above target, while rounding to nearest lets the actual riser land closer to whatever was originally entered, in either direction.
- 6-8 in riser / 9-14 in run field limits
- Trade convention for the range of values this calculator's target-rise and target-run fields accept; entering a value at the edge of that range does not itself guarantee a code-compliant stair, since code minimums and maximums vary by jurisdiction and by interior/exterior use.
Worked examples
A short exterior porch stoop, 24 inches of total rise
| Total rise (floor to floor) | 24 in |
|---|---|
| Target rise per step | 6 in |
| Target run per step | 13 in |
| Number of steps | 4 steps |
|---|---|
| Actual rise per step | 6 in |
| Run per step | 13 in |
| Comfort check (2R+T) | 25 |
24 inches divided by a 6 inch target rise comes out to exactly 4 steps with no rounding adjustment at all — the actual rise stays at 6 inches, and against a 13 inch run the comfort check lands at exactly 25, right at the edge of the accepted range.
Landing exactly on 25 here is a coincidence of round numbers, not a guarantee — nudging the run to 14 inches on the same 6 inch rise would push the comfort figure to 26 and outside the range, which is worth testing deliberately before cutting stringers rather than assuming a small run change is harmless.
A full interior flight, 112 inches floor to floor
| Total rise (floor to floor) | 112 in |
|---|---|
| Target rise per step | 7.25 in |
| Target run per step | 10.75 in |
| Number of steps | 15 steps |
|---|---|
| Actual rise per step | 7.47 in |
| Run per step | 10.75 in |
| Comfort check (2R+T) | 25.7 |
112 inches over a 7.25 inch target rise divides out to 15.45, rounding to 15 steps — which pushes the actual rise UP to 7.47 inches, half an inch taller than targeted, because rounding down in step count always means rounding up in riser height.
That recomputed 7.47 inch rise carries into the comfort check: 2×7.47+10.75 = 25.7, outside the standard range — and the original 7.25/10.75 target pair was already borderline before any rounding (2×7.25+10.75 = 25.25), so the step-count rounding didn't create the problem here, it made an already-marginal target pair worse.
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.
Where to go next
The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.