Published August 11, 2026 · Updated August 23, 2026 · By Tupep
Total rise is not what you measured
Somebody hands you a basement with an 8 ft drop and asks how many steps. The temptation is to divide 96 by 7 and call it fourteen. The problem is that 96 in is almost never the number you should be dividing. Total rise is measured from finished floor to finished floor, and on a basement stair neither of those floors exists yet when we cut the stringers.
Work it as an adjustment. Take the measurement you can actually make, from the upstairs subfloor down to the bare slab, then correct it.
| Element | Effect on total rise | Example |
|---|---|---|
| Measured subfloor to bare slab | Starting point | 96.00 in |
| Finish flooring to be added upstairs | Adds its thickness | +0.75 in engineered wood |
| Underlayment upstairs | Adds | +0.00 in, none planned |
| Finish flooring to be added on the slab | Subtracts its thickness | -0.50 in LVP with pad |
| True total rise | 96.25 in |
That 3/4 in of hardwood somebody adds two years later is not a rounding error. It lands entirely on the top riser, which is where a code inspection and a human toe both notice it.
The riser formula
- Riser count = total rise / target riser height, rounded to a whole number
- Actual riser = total rise / riser count, and this must divide out to equal risers
- Tread count = riser count minus 1, because the upper floor is the last tread
- Total run = tread count x tread run
The second line is the one that gets violated. You cannot cut twelve risers at a convenient 7.5 in and let the leftover land at the bottom. Total rise divided by riser count is the riser height, and every riser in the flight gets that number.
Worked example on 96.25 in
| Risers | Riser height | Treads | Total run at 10 in | Comment |
|---|---|---|---|---|
| 11 | 8.750 in | 10 | 100 in | Well above common residential limits |
| 12 | 8.021 in | 11 | 110 in | Still likely over the limit in many places |
| 13 | 7.404 in | 12 | 120 in | Usually the practical answer |
| 14 | 6.875 in | 13 | 130 in | Comfortable, needs 10 more inches of floor |
| 15 | 6.417 in | 14 | 140 in | Gentle, eats a lot of basement |
Thirteen risers at 7.404 in, which is about 7-13/32, is the sensible pick. Maximum riser height and minimum tread depth are set by your local code and are not the same everywhere. Many residential codes limit risers to somewhere around 7-3/4 in and require a tread depth in the 10 in range, but verify the exact numbers with your building department before cutting anything. Most codes also limit how much the tallest and shortest riser in a single flight may differ, commonly a small fraction of an inch, which is another reason the division has to come out equal.
The headroom trap
A basement stair runs underneath the floor it comes from, so the floor structure above becomes a ceiling you duck under. Headroom is measured vertically from the sloped line connecting the tread nosings up to whatever is above, and a common minimum is around 6 ft 8 in, but confirm the figure that applies to you.
Say the floor above is a 9-1/4 in joist plus 3/4 in subfloor plus 1/2 in of drywall, so the finished ceiling sits 10.5 in below the upper floor surface. Walking down, the nosing line drops 7.404 in for every 10 in of horizontal travel. Headroom at a horizontal distance d from the top is:
headroom = (7.404 x d / 10) minus 10.5
Set that to 80 in: 7.404d / 10 = 90.5, so d = 122.2 in. But the total run is only 120 in. The stairwell opening has to extend the entire length of the stair and a couple of inches past the bottom riser. At d = 120, headroom is 88.85 minus 10.5 = 78.35 in, which is short.
Check the framing plan against that number before you frame the opening. We have seen more basement stairs fail on headroom than on riser height, because the riser math is obvious and the opening length is not.
The counterintuitive part
Going to gentler risers makes headroom worse. Fourteen risers at 6.875 in requires 6.875d / 10 = 90.5, so d = 131.6 in, while the total run only grows to 130 in. You descend more slowly, so you need more horizontal distance to get your head clear of the header. If headroom is your constraint, steeper helps and shallower hurts.
Stringer throat
A cut stringer is a 2×12 with triangles removed, and what is left behind the notch is the throat. Its depth is the perpendicular distance from the inside notch corner back to the uncut edge, and it carries the stair.
For a 7.404 in rise and a 10 in run, the step hypotenuse is the square root of (54.82 + 100), which is 12.44 in. Throat lost to the notch = rise x run / hypotenuse = 74.04 / 12.44 = 5.95 in. A 2×12 is 11.25 in wide, so throat = 11.25 minus 5.95 = 5.30 in. A common guideline is to keep at least about 5 in of throat, but confirm the requirement locally. Notice how quickly this tightens: a deeper tread run eats more throat, and at some point you are buying 2×14 stock or switching to a housed stringer.
Two things to do before cutting
Measure the total rise in at least three places along the stair location. Basement slabs are poured to drain and are rarely flat, and a 1/2 in dish where the bottom riser lands changes your riser height. Use the measurement at the actual stair footprint, not the middle of the room.
Write the finish floor plan down and tape it to the stringer stock. If someone chooses tile instead of vinyl after the stair is built, the bottom riser changes and the flight becomes non-compliant. Finish floors are part of the stair calculation.
Related guides
- Deck Stair Stringer Layout: Rise, Run, and Code
- Why 7-11 Is the Rule
- How Many Deck Boards for a 12×16 Deck
- How Much Baseboard for a 3-Bedroom House
Sources and Further Reading
Run your own numbers with the Stair Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 23, 2026
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