Stair Calculator (USA)
Work out riser height, tread depth, total run, stringer length and stair angle, check them against IRC code limits, and download a professional PDF with a step-by-step marking schedule.
| Step | Riser | Height from floor | Tread | Run from start |
|---|---|---|---|---|
| Calculate to see schedule | ||||
The highlighted row is the top landing (arrival at the upper floor). Heights are measured from the lower finished floor; run is measured horizontally from the face of the first riser.
How to use the stair calculator
Four quick steps turn your total rise into a full stair layout — balanced risers, treads, total run, stringer length, and pitch — checked against IRC code limits, with a marking schedule and a downloadable PDF.
Enter the total rise
Measure finished floor to finished floor — this is the single number the whole stair is built from.
Set riser & tread
Choose a target riser height and tread depth; the calculator balances the risers evenly.
Add width & headroom
Enter stair width, nosing, and available headroom so it can run the code checks.
Read results & save a PDF
Get the step count, run, stringer, angle, a code compliance check, and a step-by-step schedule.
How the stair layout is calculated
A staircase is set by two numbers — the total rise and how you split it into steps. The calculator divides the rise into equal risers, sets the run from the tread depth, and works out the stringer, the angle, and whether it all meets code. Here is the exact math.
Worked example — a 9-ft (108″) rise, 7½″ target riser, 10″ tread
Risers: 108 ÷ 7.5 = 14.4 → 14
Actual riser: 108 ÷ 14 ≈ 7 11/16″
Treads: 14 − 1 = 13, Run: 13 × 10 = 130″
Stringer: √(108² + 130²) ≈ 169″, Angle: arctan(108 ÷ 130) ≈ 39.7°
14 steps at ~7 11/16″, 13 treads, run 10′-10″, stringer ~14′-1″, pitch 39.7° — and 2R + T = 25.4″.
Stair layout charts
Handy lookups for the questions people ask most — the IRC code limits, step counts by floor height, comfortable riser and tread pairs, and what each stair angle feels like. Confirm every figure against your local adopted code.
| Requirement | IRC limit | Notes |
|---|---|---|
| Max riser height | 7¾″ | Uniform, ≤3/8″ variation |
| Min tread depth | 10″ | Measured nosing to nosing |
| Min stair width | 36″ | Above the handrail |
| Min headroom | 6′-8″ (80″) | Measured vertically |
| Handrail height | 34″–38″ | Above the nosing |
| Nosing | ¾″–1¼″ | Where treads under 11″ |
Common IRC residential values. Codes are adopted and amended locally, and commercial stairs follow different limits — always confirm with your building department.
| Total rise | Risers | Riser height | Treads | Total run |
|---|---|---|---|---|
| 3′-0″ (36″) | 5 | 7 3/16″ | 4 | 3′-4″ |
| 6′-0″ (72″) | 10 | 7 3/16″ | 9 | 7′-6″ |
| 8′-0″ (96″) | 13 | 7 3/8″ | 12 | 10′-0″ |
| 9′-0″ (108″) | 14 | 7 11/16″ | 13 | 10′-10″ |
| 10′-0″ (120″) | 16 | 7½″ | 15 | 12′-6″ |
Using a 7½″ target riser and a 10″ tread. Your actual riser is the rise divided evenly by the step count, so it lands near — not exactly on — the target.
| Riser | Tread | 2R + T | Feel |
|---|---|---|---|
| 6½″ | 12″ | 25″ | Gentle |
| 7″ | 11″ | 25″ | Comfortable |
| 7¼″ | 10½″ | 25″ | Comfortable |
| 7½″ | 10″ | 25″ | Standard |
| 7¾″ | 10″ | 25½″ | Steepest IRC-legal |
The 2R + T comfort rule targets about 24–25″. A taller riser needs a shallower tread to stay in range, which also makes the stair steeper.
| Angle | Feel | Typical use |
|---|---|---|
| Under 30° | Gentle | Grand entries, exterior steps |
| 30°–37° | Comfortable | Ideal for most homes |
| 37°–42° | Steep | Legal but tiring; tight spaces |
| Over 42° | Very steep | Lofts & ships; not main stairs |
The angle is the rise over the run. Steeper stairs save floor space but are harder to climb and to move furniture on — most homes aim for the 30–37° band.
rise ÷ riser
treads × tread
rise ÷ run
Every stair comes from splitting one total rise into equal steps — the run and the pitch follow from there.
- Steps — rise divided by your target riser, rounded, then balanced so every riser is equal.
- Run — treads times tread depth; more steps means a longer, gentler stair.
- Stringer & pitch — the diagonal is √(rise² + run²), and its angle is the stair’s steepness.
Everything the calculator works out
One total rise gives you a complete stair layout — the step count, the geometry, a code check, and a cutting schedule you can take to the saw.
Key IRC figures every stair depends on
Built for any set of stairs
From deck steps to a basement stair or a remodel, the same calculator balances the risers, sets the run, and checks the layout against code.
Building deck steps or a basement stair and wants a safe, code-friendly layout and a clear cut list.
- Measure the total rise carefully
- Keep risers within 7¾″
- Save the PDF schedule to mark stringers
Cutting stringers on the job and needs balanced risers, run, stringer length, and a marking schedule fast.
- Balance risers to the exact rise
- Read the run and stringer
- Hand the schedule to the crew
Fitting a stair into a set opening and balancing pitch, run, and headroom against the space available.
- Trade angle against total run
- Check headroom before framing
- Confirm the layout with the AHJ
7 tips for an accurate stair layout
Small habits keep your steps uniform, your stair walkable, and your inspector happy.
Stair calculator FAQ
The step-count, code, stringer, and comfort questions people ask most before laying out a stair.
Divide the total rise, measured finished floor to finished floor, by your target riser height, then round to the nearest whole number. That gives the number of risers (steps). The number of treads is one less, because the top landing isn’t a tread.
For example, a 9-foot (108-inch) rise divided by a 7.5-inch target gives 14.4, which rounds to 14 risers at about 7 11/16 inches each, with 13 treads. The calculator balances the risers so every step is equal.
Under the IRC, the maximum riser height is 7 3/4 inches and the minimum tread depth is 10 inches, measured nosing to nosing. Risers and treads must be uniform, with no more than 3/8 inch variation across the flight.
Local codes can differ and commercial stairs follow different limits, so confirm with your building department. Comfortable residential stairs often use a 7 to 7.5 inch riser with a 10 to 11 inch tread.
The stringer follows the diagonal of the stair, so its length is the square root of the total rise squared plus the total run squared. Total run is the number of treads times the tread depth.
For a 108-inch rise and a 130-inch run, the stringer is roughly √(108² + 130²), about 169 inches, or 14 feet 1 inch. Add length for the top and bottom cuts and any overhang when buying material.
Comfortable stairs usually fall between about 30 and 37 degrees, with 30 to 35 degrees widely considered ideal. Steeper flights up to around 42 degrees are still walkable and often code-legal, but they feel harder to climb.
The angle comes from the rise over the run: a taller riser with a shallower tread gives a steeper stair. The calculator shows the pitch so you can trade comfort against the run you have room for.
The 2R + T rule is a comfort guide: twice the riser height plus the tread depth should land near 24 to 25 inches. It reflects the natural length of a person’s stride going up or down stairs.
A 7.5-inch riser with a 10-inch tread gives 2(7.5) + 10 = 25″, right in the sweet spot. Combinations far outside 24 to 25 inches tend to feel cramped or stretched underfoot.
The IRC minimum stair width is 36 inches above the handrail, and the minimum headroom is 6 feet 8 inches (80 inches), measured vertically from the tread nosing. Handrails typically sit 34 to 38 inches above the nosing.
Wider stairs feel more comfortable and make it easier to move furniture, but 36 inches is the code floor for most residential stairs. Confirm handrail and guard requirements with your local code.
Uniform steps are a safety requirement. People build a rhythm as they climb, and a single odd step is a common trip hazard. The IRC limits the variation between the largest and smallest riser, and tread, to 3/8 inch across a flight.
That’s why the calculator divides the total rise evenly rather than leaving a short step at the top or bottom. Always mark the actual balanced riser, not the target you typed in.
The calculator checks your layout against common IRC residential limits — riser, tread, width, headroom, and the 2R + T comfort range — and flags anything outside them. It’s a planning aid, not a code ruling.
Adopted codes vary by state and city, and inspectors have the final say, so confirm the layout with your building department and have a licensed professional verify it before you cut stringers.
General Estimating Notice: This calculator estimates stair geometry — riser height, tread depth, total run, stringer length, and pitch — and checks it against common IRC residential limits (max riser 7¾″, min tread 10″, min width 36″, min headroom 6′-8″). Adopted building codes vary by location and inspectors have the final say. This is a planning aid only — always confirm the layout against your local adopted code and have a licensed professional verify the final design before cutting stringers. For planning purposes only.
