Enter the floor-to-floor height and get every number you need to cut a stringer — riser count, exact riser height, total run, stringer length and angle — checked against code limits.
Measure from the top of the lower finished floor to the top of the upper finished floor, including both floor coverings.
7 to 7½ inches (18–19 cm) is the comfortable range. The calculator adjusts to whatever divides evenly.
The lip projecting past the riser below. Nosing adds walking surface but does not add to the total run.
Riser height
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Number of risers—
Number of treads—
Total run (horizontal)—
Stringer length—
Stair angle—
Walking surface per tread—
Riser + tread (comfort rule)—
Stringer stock needed—
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Code figures shown are the common IRC residential limits. Always confirm against the code adopted in your jurisdiction before cutting.
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How a stair is laid out
Everything follows from one measurement: the total rise, floor surface to floor surface. Divide it by a comfortable riser height, round to a whole number — you cannot have a fraction of a step — then divide the total rise back by that whole number to get the exact riser height. That last step is the one that matters: every riser must be identical.
There is always one fewer tread than riser on a standard flight, because the top riser lands you on the upper floor rather than on another tread. Fifteen risers means fourteen treads.
Code limits, IRC residential
Item
Limit
Maximum riser height
7¾ in (196 mm)
Minimum tread depth
10 in (254 mm)
Maximum variation between risers
⅜ in (9.5 mm)
Minimum headroom
6 ft 8 in (2032 mm)
Minimum width above handrail
36 in (914 mm)
Nosing projection
¾ to 1¼ in where treads are under 11 in
Commercial stairs under the IBC are stricter — typically 7 in maximum rise and 11 in minimum tread.
The comfort rules
Two old carpenter's formulas still hold up. Rise + run should land between 17 and 18 inches, and 2 × rise + run should land between 24 and 25 inches. A 7¼ in riser with a 10½ in tread gives 17¾ and 25 — right in the pocket. Stairs that fail these feel wrong underfoot even when they pass code.
The single most common stair fault, and the most dangerous, is a first or last step that differs from the rest. It happens when the total rise is measured to the subfloor and then flooring is added later at one end only — half an inch of tile at the bottom turns a compliant flight into a trip hazard. Always measure between finished surfaces, and if the flooring is not down yet, add its thickness before you cut. Code allows only ⅜ in of variation across the whole flight for exactly this reason.
Stringer stock and headroom
The stringer length above is the diagonal of the rise-and-run triangle. Buy stock a foot or so longer to allow for the plumb cut at the top, the seat cut at the bottom, and a mistake. Cutting a stringer removes a lot of material, so use 2×12 rather than 2×10 for anything but a shallow flight — the remaining throat under the notches is what carries the load.
Headroom is measured vertically from the tread nosing line to whatever is above, and a steep flight in a tight opening is where it usually fails. Check it before framing the floor opening, not after.
A riser of 7 to 7½ inches with a tread of 10 to 11 inches is the comfortable residential standard. IRC limits are 7¾ in maximum rise and 10 in minimum tread; commercial stairs under the IBC are typically 7 in and 11 in.
How many steps for an 8 foot ceiling?
With a floor-to-floor height around 105 to 109 inches once joists and flooring are included, you would use 15 risers of about 7¼ inches each, giving 14 treads and a total run of about 12 feet at a 10½ inch tread.
How do I calculate stringer length?
It is the hypotenuse of the total rise and total run: stringer = √(rise² + run²). A 108 inch rise with a 147 inch run gives about 182 inches, or roughly 15 feet 2 inches, before allowing for the end cuts.
Do all the risers have to be the same height?
Yes — this is a strict code requirement, with no more than ⅜ inch difference between the tallest and shortest in a flight. Uneven risers are the leading cause of stair falls, because people stop looking at their feet after the first two steps.
Does nosing count toward the tread depth?
Tread depth is measured from nosing to nosing, so the overhang does not add to the total run of the stair — but it does add usable walking surface. Where treads are less than 11 inches deep, the IRC requires a nosing of ¾ to 1¼ inches.