A Free Tool · Steps, Riser & Run · IRC Code Checks
How many stairs do you actually need?
Enter the total rise — the finished floor-to-floor height your stairs have to climb
— and get the number of steps, the actual riser height, the number of treads, the
total run, and the stringer length. The calculator also flags your design against the
IRC residential limits: a 7.75″ maximum riser and a 10″ minimum tread.
Read this first
This is a planning estimate, not an engineered stair design. It assumes one straight flight
with equal risers and a level run, and it does not size landings, headroom, handrails, or
winders. Stairs are one of the most code-regulated parts of a house. Always confirm the
riser, tread, headroom, and handrail requirements with your local building
code — which can be stricter than the IRC — and pull the required
permits before you cut a single stringer.
The calculator
Calculate your stairs
Enter the total floor-to-floor rise in inches, a comfortable target riser height, and your planned tread depth. You'll get the buildable number of steps, the actual riser height once the count is rounded to whole steps, the tread count, the total run, and the stringer length — plus a code check.
Finished floor-to-floor vertical height. An 8′ floor-to-floor is roughly 108″.
Your comfort target; about 7–7.5″ is typical. The actual height is back-calculated.
Horizontal depth of each step. IRC minimum is 10″.
Number of steps (risers)
Actual riser height
Number of treads
Total run
Stringer length
The math, honestly
How it works
Everything starts from the total rise — the floor-to-floor height.
You can't build a fractional step, so the calculator first divides the rise by your
target riser and rounds to the nearest whole number:
steps = round(total_rise / target_riser). That whole number is the count of
risers, also called steps.
Because the count is forced to a whole number, the actual riser height
almost never equals the target you typed. It's back-calculated:
actual_riser = total_rise / steps. Every riser in the flight has to be this
same height — building code allows almost no variation between steps. There is
always one fewer tread than risers (treads = steps − 1),
because the top landing is the last step up, so the total run is
treads × tread_depth.
The stringer is the diagonal board the steps are cut into, and its
length is pure Pythagoras: √(total_rise² + total_run²),
then divided by 12 for feet. For a 108″ rise with 13 treads at 10″, the run is
130″, so the stringer is √(108² + 130²) = √28,564 ≈
169″, about 14.1 feet. Buy the board a little longer to leave room for the
end cuts and notch depth.
Common total rises
Worked examples at a 7.5″ target riser and a 10″ tread, computed with the same
formulas the calculator uses — so these match what the tool gives you. The actual
riser is the total rise divided by the rounded step count; treads are one fewer than steps.
Total rise
Stepsrisers
Actual risertotal rise ÷ steps
Total runtreads × 10″
Stringerdiagonal
96″ (8′)
13
7.38″
120″
153.7″ (12.8′)
104″
14
7.43″
130″
166.5″ (13.9′)
108″ (9′)
14
7.71″
130″
169.0″ (14.1′)
112″
15
7.47″
140″
179.2″ (14.9′)
120″ (10′)
16
7.50″
150″
192.1″ (16.0′)
Every actual riser above is at or under the IRC 7.75″ maximum, and the 10″ tread
meets the minimum. The 96″ and 120″ rows are labeled with their rough
floor-to-floor heights; always measure your real rise rather than assuming, since flooring
buildup and framing change it.
The 7-11 rule
A quick comfort target carpenters lean on, and how it relates to the actual code limits.
What 7-11 means
The 7-11 rule says aim for a 7″ riser with an 11″ tread. It sits comfortably inside the IRC limits — a riser no taller than 7.75″ and a tread no shallower than 10″ — and lands in the zone most people find easy to climb. It's a guideline, not the code itself: the code states the maximum riser and minimum tread, and 7-11 just aims for the sweet spot between them.
The 'rise + run' check
Two related rules of thumb cross-check comfort. Rise + run (one riser plus one tread) should fall roughly between 17 and 18 inches. 2R + T (twice the riser plus one tread) should land near 24 to 25 inches. A 7″ riser with an 11″ tread gives 18 and 25 — right on target. These encode the natural relationship between how high your foot lifts and how far it steps forward.
Why steeper still passes
Stairs with a 7.71″ riser and a 10″ tread — like our 108″ example — are fully legal, but they're steeper than 7-11 and feel a touch harder to climb. The code sets the outer boundary; 7-11 sets the comfort target. If you have the horizontal space, a deeper tread and a slightly shorter riser make the climb noticeably easier, especially for kids and older adults.
Where to buy
Got your numbers? Here's where to pick up what you need:
The terms behind the calculator, in plain English. These are background definitions, not
engineering specifications — follow your local building code and any engineered plan
for the real thing.
Total rise
The full vertical height a flight of stairs has to climb, measured from one finished floor to the next finished floor — not the ceiling height. It is the single input everything else is derived from. Flooring buildup and framing change it, so always measure the real finished-to-finished height.
Riser
The vertical face of a single step, and its height. The number of risers equals the number of steps. The IRC caps the riser height at 7.75 inches, and every riser in a flight must be within about 3/8 inch of every other.
Step (number of steps)
One step up equals one riser, so "number of steps" and "number of risers" mean the same count. You can't build a fractional step, which is why the count is rounded to a whole number and the actual riser height is then back-calculated from it.
Tread (run)
The horizontal surface you step on, and its depth front-to-back — also called the run of a single step. The IRC requires a tread depth of at least 10 inches. There is always one fewer tread than risers, because the top landing serves as the last step.
Total run
The total horizontal distance the staircase covers, equal to the number of treads times the tread depth. It tells you how much floor space the flight will eat up — often the constraint that decides whether a staircase fits at all.
Stringer
The diagonal structural board the treads and risers are cut into or attached to. Its length is the diagonal of the rise-and-run triangle: √(total rise² + total run²). Buy the lumber a little longer than the bare diagonal to allow for the end cuts and the depth of the notches.
IRC (residential code)
The International Residential Code, the model code most U.S. jurisdictions base their rules on. For stairs it sets a maximum riser of 7.75″, a minimum tread of 10″, minimum headroom of 6′8″, and rules for handrails and landings. Local codes can be stricter, so always confirm with your building department.
Frequently asked
It depends on the total floor-to-floor rise, not the ceiling height alone. A common 8-foot floor-to-floor height with framing and flooring works out to roughly 108 inches of total rise. At a 7.5″ target riser, that's 108 ÷ 7.5 = 14.4, which rounds to 14 risers (steps). The actual riser height is then 108 ÷ 14 = about 7.71″, within the IRC 7.75″ maximum, with 13 treads. Always measure your real rise rather than assuming. Try it in the calculator.
A riser of about 7 to 7.5 inches with a tread of about 10 to 11 inches is widely considered comfortable. The IRC caps the riser at 7.75″ and requires a tread of at least 10″, so a comfortable stair sits just inside those limits. Steeper stairs — taller risers, shallower treads — are legal up to the limits but feel harder to climb, especially going down.
The 7-11 rule is a quick comfort target: a 7″ riser with an 11″ tread. It sits comfortably inside the IRC limits (riser no more than 7.75″, tread no less than 10″) and produces stairs most people find easy to climb. It's a guideline, not the code itself — the code states the maximum riser and minimum tread, and 7-11 lands in the sweet spot between them.
The stringer length is the diagonal, found with the Pythagorean theorem: √(total rise² + total run²). For a 108″ total rise with 13 treads at 10″ each, the total run is 130″, so the stringer is √(108² + 130²) = √28,564 = about 169″, or roughly 14.1 feet. Buy lumber a bit longer than the bare diagonal to allow for the top and bottom cuts and the depth of the notches.
Under the International Residential Code, the maximum riser height is 7.75″ and the minimum tread depth is 10″. The code also limits the variation between the tallest and shortest riser (and between treads) in one flight to about 3/8″, requires headroom of at least 6′8″, and has rules for handrails and landings. Local codes can be stricter or differ, so always confirm with your local building department and pull the required permits.
Because the top of the flight is a landing or floor, not a tread. As you climb, each riser is a step up, but the last step up lands you on the upper floor itself, so that final riser has no tread board in front of it. A flight with 14 risers therefore has 13 treads. This is why the total run uses the tread count, not the riser count.
It's a comfort check: the sum of one riser plus one tread should fall roughly between 17 and 18 inches. A related rule, 2R + T (twice the riser plus one tread), should land near 24 to 25 inches. Both encode the natural relationship between how far your foot lifts and how far it steps forward. Stairs that satisfy these feel even and unhurried; stairs well outside them feel either cramped or like a ladder.
Because you can't build a fractional step. You divide the total rise by your target riser to get an ideal step count, but that almost never comes out whole. Rounding to the nearest whole number gives a buildable count, and then the actual riser height is recomputed by dividing the total rise by that whole count. That's why your actual riser usually differs slightly from the target you typed — the math is forced to land on equal, whole steps.