Stair Calculator
Risers, treads, exact riser height, total run, stringer length and angle from your total rise — checked against IRC R311.7 limits and the 2R+T comfort rule.
Stair Calculator: with the default inputs, number of risers is 15.
Finished floor to finished floor (or deck to grade). Measure with a level and a straight edge, not along the slope.
7–7½ in is comfortable indoors; code maximum is 7¾ in (IRC R311.7.5.1).
Nosing to nosing, excluding the overhang. Code minimum 10 in (IRC R311.7.5.2); 10½–11 in is more comfortable.
- Actual riser height
- 7.2 in
- Number of treads
- 14
- Total run
- 140 in
- Stringer length
- 14.73 ftHypotenuse of total rise and total run; buy stock at least this long plus the top and bottom cuts.
- Stair angle
- 37.6 deg30–37° is the comfortable range for a residential stair.
- 2 × riser + tread (inches)
- 24.4Comfort rule of thumb: 24–25 in.
- Max tread depth that fits the run limit
- —Only when a run limit is set.
Assumptions
- Riser count is rounded to the nearest whole number from your desired riser height; the calculator warns if that exceeds 7¾ in.
- Tread depth is the horizontal run per step, nosing to nosing; the nosing overhang is not added to total run.
- Code limits are the 2021 IRC; local amendments may differ.
| Item | Limit | Section |
|---|---|---|
| Maximum riser height | 7¾ in (196 mm) | R311.7.5.1 |
| Minimum tread depth | 10 in (254 mm) | R311.7.5.2 |
| Nosing | ¾–1¼ in, required if tread < 11 in | R311.7.5.3 |
| Variation between risers or treads | ≤ 3/8 in within a flight | R311.7.5.1–2 |
| Minimum clear width | 36 in above the handrail | R311.7.1 |
| Minimum headroom | 6 ft 8 in (2,032 mm) | R311.7.2 |
| Handrail height | 34–38 in above nosings | R311.7.8.1 |
Local amendments vary — some states use 8¼ in / 9 in (older BOCA/UBC). Check with your building department.
How this is worked out
The formula
Risers = round(total rise ÷ desired riser) Actual riser = total rise ÷ risers Treads = risers − 1 (floor above is the last tread) Total run = treads × tread depth Stringer length = √(total rise² + total run²) Angle = arctan(total rise ÷ total run) Comfort: 2 × riser + tread ≈ 24–25 in
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Total rise
- Finished floor to finished floor (or deck to grade). Measure with a level and a straight edge, not along the slope.in in, ft, cm, mm, m · 0.1 or more · defaults to 108
- Desired riser height
- 7–7½ in is comfortable indoors; code maximum is 7¾ in (IRC R311.7.5.1).in in, cm, mm · from 0.5 to 20 · defaults to 7.25
- Tread depth (run per step)
- Nosing to nosing, excluding the overhang. Code minimum 10 in (IRC R311.7.5.2); 10½–11 in is more comfortable.in in, cm, mm · 1 or more · defaults to 10
- Maximum total run available(under More options)
- Horizontal space you have for the stair. Leave 0 for no limit; if set, you'll get the tread depth that fits.in ft, in, m, cm · 0 or more · defaults to 0
- Top step is a tread (not the landing)(under More options)
- Off: the upper floor serves as the last tread, so treads = risers − 1 (usual). On: treads = risers, as when the stringer ends below a deck rim.defaults to off
What you get back
- Number of risersmain answer
- Actual riser height
- Number of treads
- Total run
- Stringer length
- Hypotenuse of total rise and total run; buy stock at least this long plus the top and bottom cuts.
- Stair angle
- 30–37° is the comfortable range for a residential stair.
- 2 × riser + tread (inches)
- Comfort rule of thumb: 24–25 in.
- Max tread depth that fits the run limit
- Only when a run limit is set.
What this assumes
- Riser count is rounded to the nearest whole number from your desired riser height; the calculator warns if that exceeds 7¾ in.
- Tread depth is the horizontal run per step, nosing to nosing; the nosing overhang is not added to total run.
- Code limits are the 2021 IRC; local amendments may differ.
About this calculator
Stairs are laid out backwards from the one number you can't change: the total rise from finished floor to finished floor. Divide it by a comfortable riser, round to a whole number of risers, and the exact riser height follows. This calculator does that, works out treads, total run, stringer length and angle, then checks the result against the residential code limits so you find out about a problem before you cut a $40 stringer.
Measure the total rise correctly
Measure vertically from the lower finished floor to the upper finished floor — not to the subfloor and not along the slope. On a deck, measure from the top of the decking to where the bottom step will land, and if the ground slopes, use a level and a long straight edge to project out to that spot. Being ½ in off on total rise puts every riser out by a fraction, and the 3/8-in variation limit is one of the most-failed inspection items.
Remember to account for finish flooring that isn't down yet: if the upper floor gets ¾-in hardwood and the lower floor tile, the total rise changes.
Choosing riser and tread
- Riser: 7 to 7½ in feels right indoors; 7¾ in is the IRC maximum (R311.7.5.1). Exterior and deck stairs are often 6–7 in.
- Tread: 10 in is the code minimum (R311.7.5.2); 10½–11 in is noticeably more comfortable and what most finish carpenters aim for. The tread depth here is nosing-to-nosing run, not the board width — a 1-in nosing sits on top of that.
- The old carpenter's rule: two risers plus one tread should be 24–25 in. A 7¼ × 10½ stair is 25. Keep that sum and the stair will feel natural even if you trade rise for run.
Fitting the stair in the space
If the run is limited by a wall or a doorway, enter it under More options. The calculator will tell you the deepest tread that fits, and warn you if that pushes you under 10 in — at which point you need a landing and a turn, a taller riser (if you're under 7¾), or a different location.
From numbers to stringers
Lay out the riser height and tread depth on a framing square with stair gauges, step it off along a 2×12, then drop the bottom of the stringer by one tread thickness so the first and last risers come out equal once the treads are on. The stringer length shown is the hypotenuse; buy stock a foot or two longer for the plumb and level cuts at each end.
Frequently asked questions
▸How many steps do I need for a 9-foot ceiling?
Total rise is floor to floor, so with a 9-ft ceiling and 12 in of floor structure it's about 120 in. At a 7½-in riser that's 16 risers (7.5 in each) and 15 treads — 12.5 ft of run at 10 in per tread.
▸What is the maximum riser height by code?
7¾ in (196 mm) under the International Residential Code, section R311.7.5.1, with no more than 3/8 in variation between the tallest and shortest riser in a flight. Some jurisdictions still allow 8¼ in — check locally.
▸What is the minimum tread depth?
10 in (254 mm) measured nosing to nosing, per IRC R311.7.5.2. If treads are under 11 in, a nosing of ¾ to 1¼ in is required.
▸Why is the number of treads one less than the risers?
Because the upper floor acts as the top tread. You step up the last riser onto the floor itself. The exception is a stair that ends below a deck rim, where the stringer carries a final tread — turn on 'Top step is a tread' for that.
▸How long a board do I need for stringers?
The stringer length is the hypotenuse of total rise and total run — for a 108-in rise and 140-in run, 177 in (14.75 ft). Buy 16-ft 2×12s to allow for the cuts at each end.
Put this calculator on your own site
A working stairs, free for any site, with no ads and no sign-up. It resizes to fit wherever you paste it and updates itself as this page improves.
Paste this anywhere. It works on any site, carries no ads, never expires, and always shows the current version.
Stair Calculator by CalculateItNow
The page's own title. The clearest description of what the link leads to.
The credit line sits outside the widget on purpose, so it is a real link on your page rather than one buried in a frame. Please keep it — it is what pays for CalculateItNow staying free and ad-free. The script only resizes the widget to fit its contents; drop it and the widget still works.
Browse every calculator widget·How to add it to WordPress, Squarespace or Wix
Related calculators
The questions people ask next to a stairs.
Convert rise and run to roof pitch (x:12), degrees and slope percent, get the pitch multiplier, and turn a footprint into real roof area and squares.
Cubic yards of concrete for slabs, footings, round columns and stairs, plus 60-lb and 80-lb bag counts (Quikrete yields), weight and cost — with the math shown.
Board feet from thickness, width, length and quantity, with cost per board foot, nominal vs actual sizes explained and a table of common dimensional lumber.
Convert between inches, feet, yards, miles, millimeters, centimeters, meters, kilometers and nautical miles — all at once, with exact factors and a reference table.
Posts, rails, pickets and concrete bags for a fence from its length, post spacing and gates — Quikrete-based bag counts, picket spacing and a materials cost.