Stair Rise and Run Calculator
| Total rise | Risers | Riser height | Total run (10" treads) |
|---|---|---|---|
| 96" (8 ft wall) | 13 | 7.38" | 120" |
| 102" | 14 | 7.29" | 130" |
| 108" (9 ft wall) | 14 | 7.71" | 130" |
| 120" (10 ft wall) | 16 | 7.50" | 150" |
A staircase is one division done well: take the floor-to-floor rise, split it into equal risers inside the 7-to-7.75 inch band that legs expect, and the step count stops being a guess. Get the split right and every tread lands where the body predicts; get it wrong by a quarter inch and every seventh step trips someone for the life of the house.
Bottom line: divide rise by 7.75 and round up for the riser count, then re-divide for the exact riser height - a 108-inch floor-to-floor is 14 risers at 7.71 inches. Tread run follows the comfort rule (two risers plus one tread should total about 17.5 inches), and the total run tells you whether the hallway survives the design.
The honest part: code sets the bounds - risers max 7.75 inches, treads min 10 in most US codes - but comfort lives in consistency, not the maximums. A staircase with one riser an eighth-inch off its siblings is the defect inspectors flag and owners feel but can never name.
How to use
- Measure total rise floor-to-finish-floor in inches - subfloor to subfloor, not to the old floor's surface.
- Read the riser count and exact riser height; anything over 7.75 needs one more riser, anything under 7 is a luxury of space.
- Pick a tread run (10 to 11 inches is the residential band), then read the total run your floor plan must donate - and check headroom along the whole path.
Frequently asked questions
How many stairs for a 9-foot ceiling?
A 9-foot ceiling with a standard floor assembly gives a floor-to-floor rise near 108 inches: at 14 risers that is 7.71 inches each - just inside the 7.75 maximum - with 13 treads at 10 inches eating 130 inches, about 10 feet 10 inches, of total run. Eight-foot ceilings divide sweeter: 13 risers at 7.38 for the same footprint minus one tread.
What is the 2R+T rule for stairs?
Two risers plus one tread should total about 17.5 inches - the stride your leg falls into on level ground. With 7.5-inch risers the tread wants 10 inches; with a luxurious 7-inch riser, 10.5. It is why steep staircases with deep treads feel wrong: the stride math disagrees with what the eye sees.
What is the maximum riser height by code?
Most US residential codes cap risers at 7.75 inches and require treads of at least 10 inches, with the tallest and shortest riser in one flight allowed to differ by no more than 3/8 inch. Canada and the IRC agree on the consistency clause - it is the rule that actually prevents falls, and the one hand-built staircases fail.
How much headroom does a staircase need?
Six feet eight inches (80 inches) minimum, measured vertically from the tread nosing along the path of travel - and measure at every step, because the worst point is usually where the stair passes the second-floor framing or a sloped ceiling. A design that fits the run but starves the headroom becomes a duvet-bump staircase.