How to measure total rise
Total rise is the vertical distance from the finished lower floor to the finished upper floor. If the flooring isn’t down yet, measure subfloor to subfloor and add the difference in finish thickness. A stair laid out on bare subfloor that later gets 3/4 in hardwood at the top and nothing at the bottom ends up with a top riser 3/4 in shorter than the rest — more than the 3/8 in variation the IRC allows.
Measure in two or three places across the opening, because floors are rarely perfectly level. For a deck, measure from the deck surface straight down to where the bottom step will land, then check whether the ground slopes away along the run. A sloping landing area changes the rise you actually need.
Worked example: a 9 ft floor-to-floor stair
These are the calculator’s default inputs: 108 in rise, 7 3/4 in maximum riser, 10 1/2 in treads, 36 in wide, 2×12 stringers.
| Step | Calculation | Result |
|---|---|---|
| Risers | 108 ÷ 7.75 = 13.94, round up | 14 risers |
| Actual riser | 108 ÷ 14 | 7.714 in (just under 7 3/4) |
| Treads | 14 − 1 | 13 treads |
| Total run | 13 × 10.5 in | 136.5 in (11 ft 4 1/2 in) |
| Stair angle | atan(7.714 ÷ 10.5) | 36.3° |
| Stringer length | √(108² + 136.5²) | 174.1 in (14.5 ft) → 16 ft boards |
| Stringers | ceil(36 ÷ 16) + 1 | 4 |
| Throat left on a 2×12 | 11.25 − 6.22 | 5.03 in |
Notice the stringer is 14.5 ft, so 14 ft stock is too short once you allow for the plumb cut at the top and level cut at the bottom. Always buy the next length up.
Choosing a riser count
The calculator also lists the riser counts on either side of the minimum. For the same 108 in rise:
- 13 risers gives 8.308 in steps — over the 7 3/4 in limit, so not allowed.
- 14 risers gives 7.714 in steps and a 136.5 in run.
- 15 risers gives 7.2 in steps, a gentler stair, but needs 147 in of run.
Adding a riser makes each step easier to climb but costs another tread depth of floor space. If your run is tight, the minimum riser count is usually the answer; if you have room, a riser near 7 to 7 1/2 in is noticeably more comfortable for everyday use.
Laying out and cutting the stringers
- Set a framing square with stair gauges at the actual riser (7 23/32 in is close to 7.714) on the tongue and the tread depth on the blade.
- Mark every step along the board, keeping the same edge against the crown side.
- Drop the stringer: cut the thickness of one tread off the bottom so the first step isn’t taller than the others once treads go on.
- Cut the first stringer, test-fit it, then use it as a pattern for the rest.
Finish notches with a handsaw rather than overcutting with a circular saw. Overcuts reduce the throat — the solid wood below the notches — and that throat is what carries the load. The calculator warns when less than 3.5 in remains, a common rule of thumb rather than a code figure.
The code checks, in plain terms
The table checks your layout against 2021 IRC R311.7: risers no taller than 7 3/4 in, treads at least 10 in deep, at least 36 in of clear width, and a 3/4–1 1/4 in nosing when treads are less than 11 in deep. Headroom of 6 ft 8 in is measured from the sloped line of the nosings, so check it at the opening before you cut anything. Local codes can amend the IRC, so confirm with your building department.
Related tools
Building deck stairs? Price the whole deck with the deck cost calculator. If the stairs land on a new pad, size it with the concrete calculator.
How this calculator works
- Risers = total rise ÷ maximum riser, rounded up. Actual riser = total rise ÷ risers. Treads = risers − 1.
- Total run = treads × tread depth. Stair angle = arctan(riser ÷ tread).
- Stringer length = √(total rise² + total run²), matched to the next standard stock length of 8, 10, 12, 14 or 16 ft.
- Number of stringers = ceil(width ÷ 16 in) + 1.
- Throat depth = lumber depth − (riser × tread ÷ √(riser² + tread²)), the perpendicular depth left under each notch.
- Code checks compare your layout with 2021 IRC R311.7: riser ≤ 7 3/4 in, tread ≥ 10 in, width ≥ 36 in, nosing 3/4–1 1/4 in where tread < 11 in, 3/8 in max variation and 6 ft 8 in headroom.
Assumptions and limitations
- All risers are equal: total rise is divided evenly, so the top and bottom risers match only if the finished floor heights are what you measured.
- There is one fewer tread than risers; the upper floor serves as the top step.
- Stringer spacing of no more than 16 in on center is common practice for 1× and 5/4 treads, not a code requirement. Thicker treads may span farther.
- Keeping at least 3.5 in of solid stringer below the notches is common guidance, not a code number.
- Lumber depths are actual dressed sizes: 2×12 = 11 1/4 in, 2×10 = 9 1/4 in.
- The stringer length is the straight diagonal; buy longer stock to allow for the plumb and level cuts at the top and bottom.
These results are planning estimates, not quotes. Local prices, site conditions and building codes vary, so get written estimates from licensed contractors before you commit to a budget.
Try your own numbers. Every price and assumption above is editable in the estimator.
Back to the stair stringers estimatorFrequently asked questions
How many steps do I need for a 9 ft (108 in) rise?
Why is there one fewer tread than risers?
Does the riser height include the floor finish?
Sources and data
- ICC, 2021 IRC — IRC2021P3 Pt03 Ch03 SecR311.7.5.1
- ICC, 2021 IRC — IRC2021P3 Pt03 Ch03 SecR311.7.5
- ICC, 2021 IRC — IRC2021P3 Pt03 Ch03 SecR311.7.1
Prices are US national ranges reviewed October 2026 (data version 2026.10). A few values are editorial estimates where no single published source exists; the Cost Index marks each one. Read our methodology and editorial policy.