Stairs Calculator
Enter one measurement — your total rise — and get a complete, code‑compliant stair layout with a 3D diagram, stringer cut list, and printable template. Free, instant, in inches or millimeters.
Finished floor to finished floor.
Stairs Calc rounds to a whole number of equal risers and keeps them within code.
The depth you step on, not counting the nosing.
Top of the rail above the nosing line. Codes target 34–38".
A guard fills the side with your chosen infill — balusters, glass, cable, or horizontal bars. Renders live in 3D and is included in the .obj export.
Advanced inputs
Open risers leave a gap between treads — drawn live in the diagram. Some codes (ADA) require closed risers.
Steps (risers)
16
15 treads
Riser height
7 3/16"
183 mm
Tread run
11"
279 mm
Stringer length
16' 8 15/16"
5.104 m
Stair angle
33.2°
Very comfortable
Total run
13' 8 3/4"
4.185 m
Min stairwell opening
10' 11 13/16"
3.348 m
Recommended board
2x12
throat 5 1/4"
Board to buy
17' 8 15/16"
5.409 m
Comfort
Very comfortable
- Blondel pass
- Rise + Run pass
- Ideal angle pass
Cut list & framing square
Materials
| Item | Qty | Detail |
|---|---|---|
| Stringers | 3 | 2x12 cut to board length |
| Treads | 15 | tread depth 304 mm × 914 mm wide |
| Risers | 16 | riser height 183 mm × 914 mm wide |
| Fasteners | 180 | structural screws / nails (≈4 per tread-to-stringer joint) |
Framing-square settings
- Rise on tongue
- 7 3/16"
- Run on body
- 11"
- Recommended board
- 2x12
- Throat
- 5 1/4"
- Board length
- 17' 8 15/16"
- Stringers
- 3
Per-step running measurements
| Step | Cumulative rise | Cumulative run |
|---|---|---|
| 1 | 7 3/16" | 11" |
| 2 | 14 3/8" | 21 15/16" |
| 3 | 21 9/16" | 32 15/16" |
| 4 | 28 3/4" | 43 15/16" |
| 5 | 35 15/16" | 54 15/16" |
| 6 | 43 1/8" | 65 7/8" |
| 7 | 50 5/16" | 76 7/8" |
| 8 | 57 1/2" | 87 7/8" |
| 9 | 64 11/16" | 98 7/8" |
| 10 | 71 7/8" | 109 13/16" |
| 11 | 79 1/16" | 120 13/16" |
| 12 | 86 1/4" | 131 13/16" |
| 13 | 93 7/16" | 142 13/16" |
| 14 | 100 5/8" | 153 3/4" |
| 15 | 107 13/16" | 164 3/4" |
| 16 | 115" | 175 3/4" |
Cut the bottom riser shorter by 1" so every finished riser stays equal.
Save & compare designs Show Hide
Save the stair you're looking at, tweak the inputs, save another, then compare them side by side — comfort, code, and key dimensions at a glance.
Estimate the cost $1,139–$1,709
| Stringers (3) | $176 |
| Treads (15) | $270 |
| Risers (16) | $144 |
| Fasteners & hardware | $25 |
| Railing | $335 |
| Labor | $475 |
Low
$1,139
Estimate
$1,424
$89/step
High
$1,709
Rough order-of-magnitude only. Lumber, fastener and labor prices swing by region and season — the low–high band reflects that spread. For a line-item breakdown with editable prices, open the stairs cost calculator.
Not sure where to start? Design it from your space
Tell Stairs Calc what you’re working with — your total rise, how much run you can give the stair, and the ceiling clearance overhead — and it designs the most comfortable, code-compliant staircase that fits, then explains every choice. Adjust the priority toward comfort or a compact footprint, or let it turn a long flight into an L or U with a landing.
Design the perfect stairs for me
Finished floor to finished floor — the one required measurement.
How far the stair can project horizontally.
Clearance above the stair to the ceiling or opening.
Straight staircase · 16 steps
Fits your space
Steps (risers)
16
15 treads
Riser height
7 3/16"
Tread run
10"
Stair angle
35.7°
Very comfortable
Comfort
100/100
Very comfortable
Min stairwell opening
10'
headroom met
Why these stairs
- Chose 16 risers at 183 mm — the most comfortable equal-riser fit (comfort 100/100).
- Picked a 254 mm going — the run that best satisfies 2R+T for that riser.
- Headroom 2032 mm is met; the stairwell opening needs to be at least 3048 mm long.
- Total run 3.81 m fits your 4.00 m space.
- Meets IRC 2021.
How to use this stair calculator
Start by measuring your total rise — the vertical distance from the lower finished floor to the upper finished floor. Type it into the first field and Stairs Calc instantly fills in a complete, code-compliant staircase: how many steps you need, the exact height of each riser, the depth of each tread, the length of the stringer board to cut, and the staircase angle. Adjust the tread run, choose “by number of steps” if you already know how many you want, and switch between inches and millimeters at any time. The 3D diagram redraws as you type, and the Code panel checks every dimension against your selected building code so you know it’s safe before you cut a single board.
What the results mean
- Number of steps (risers)
- How many vertical risers the flight has. The number of treads is always one less, because the upper floor itself is the final step.
- Riser height
- The vertical height of each step — kept equal to the millimeter, which is what building codes require.
- Tread run (going)
- The horizontal depth you step on, not counting the nosing overhang.
- Total run
- How far the staircase projects horizontally — use this to confirm it fits your space.
- Stringer length
- The straight-line length of the sawtooth board, corner to corner; buy a board about a foot longer to allow for the top and bottom cuts.
- Stair angle
- The pitch of the flight; 30–37° is the comfortable range.
- Minimum stairwell opening
- The shortest floor opening that still gives 6′8″ of headroom.
Stair formulas (with a worked example)
- Number of risers
N = round(total rise ÷ ideal riser)Round to the nearest whole number, then divide the rise back by N for the exact, equal riser height.
- Riser height
riser = total rise ÷ N- Treads
treads = N − 1The upper floor acts as the top step.
- Total run
total run = (N − 1) × run- Stringer length
stringer = √(total rise² + total run²)The hypotenuse of the staircase triangle (Pythagoras).
- Stair angle
angle = atan(rise ÷ run)The pitch of one step.
- Minimum stairwell opening
opening = ((floor thickness + headroom) × total run) ÷ total rise- Throat
throat = board width − (rise × run) ÷ √(rise² + run²)Keep at least 3½″ of solid wood behind the notch.
- Comfort — Blondel
2 × rise + run = 24″–25″The classic stepping-cadence rule.
- Comfort — Rise + Run
rise + run = 17″–18″- Comfort — Product
rise × run ≈ 70–75 in²
Worked example — a 9′-7″ total rise
Dividing by an ideal 7" riser gives 16 risers, so each riser is 7³⁄₁₆". With a 11" run there are 15 treads, a total run of 13′-8¾″, a stringer length of 16′-9″, and an angle of 33.2° — very comfortable and within IRC limits.
Stair building codes: rise, run, headroom & handrails
Every result is checked against the building code you choose. Residential homes in the US follow the IRC (max riser 7¾″, min tread 10″); commercial buildings follow the stricter IBC (7″ riser, 11″ tread). The comfort rules go further than code: the most comfortable step is roughly a 7″ rise with an 11″ run, which satisfies both 2 × rise + run ≈ 24″–25″ and rise + run ≈ 17″–18″.
86 building codes across 6 regions. The 8 US/UK/EU codes are primary-source verified; international rows are indicative — confirm against your locally adopted code.
Swipe the table sideways to see all 11 metrics →
| Code | Max riser | Min riser | Min run (going) | Uniformity tolerance | Min headroom | Min width | Handrail height | Guard height | Guard trigger (drop) | Baluster max sphere | Max rise between landings |
|---|---|---|---|---|---|---|---|---|---|---|---|
| United States | |||||||||||
| US – Accessibility (ADA) | 7" | 4" | 11" | 3/8" | 6' 8" | 36" | 34"–38" | — | — | — | — |
| US – Commercial (IBC) | 7" | 4" | 11" | 3/8" | 6' 8" | 44" | 34"–38" | 42" | 30" | 4" | 12' |
| US – Residential (IRC) | 7 11/16" | — | 10" | 3/8" | 6' 8" | 36" | 34"–38" | 36" | 30" | 4 3/8" | 12' 7" |
| US – Workplace (OSHA) | 9 1/2" | — | 9 1/2" | — | 6' 8" | 22" | 30"–38" | 42" | — | — | — |
| Europe | |||||||||||
| Albania low confidence | 8 1/4" | 5 1/2" | 11 7/16" | — | 6' 2 13/16" | 35 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | — | 8' 3 3/16" |
| Austria high confidence | 7 1/16" | — | 10 5/8" | — | 6' 10 11/16" | 47 1/4" | 35 7/16"–43 5/16" | 39 3/8" | — | 4 3/4" | 11' 9 3/4" |
| Belarus medium confidence | 5 7/8" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | 8' 10 5/16" |
| Belgium medium confidence | 7 1/16" | — | 7 7/8" | — | — | 31 1/2" | 35 7/16"–39 3/8" | 43 5/16" | — | 4 5/16" | — |
| Bosnia and Herzegovina low confidence | 7 1/2" | — | 9 13/16" | — | 7' 2 5/8" | 43 5/16" | 35 7/16"–39 3/8" | 39 3/8" | — | 4 3/4" | 11' 2 5/8" |
| Bulgaria medium confidence | 8 11/16" | — | 9 13/16" | — | 6' 6 3/4" | 47 1/4" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 9/16" | 3' 11 1/4" |
| Croatia medium confidence | 7 1/2" | — | 9 13/16" | — | 6' 10 11/16" | 43 5/16" | 35 7/16"–35 7/16" | 39 3/8" | — | 5 1/2" | — |
| Cyprus high confidence | 7 1/16" | 5 5/16" | 11" | — | 6' 10 11/16" | 47 1/4" | 27 9/16"–35 7/16" | 43 5/16" | — | 3 15/16" | 10' 7 9/16" |
| Czechia high confidence | 7 1/2" | 5 7/8" | 8 1/4" | — | 6' 10 11/16" | 35 7/16" | 35 7/16"–47 1/4" | 39 3/8" | — | 4 3/4" | 10' 7 9/16" |
| Denmark medium confidence | 7 1/16" | — | 9 13/16" | — | 6' 10 11/16" | 39 3/8" | 31 1/2"–31 1/2" | 39 3/8" | — | 3 1/2" | — |
| Estonia low confidence | 6 5/16" | — | 10 5/8" | — | 6' 10 11/16" | 35 7/16" | 35 7/16"–35 7/16" | 39 3/8" | — | 4 5/16" | — |
| Finland high confidence | 7 1/2" | — | 9 13/16" | — | 6' 4 3/4" | 33 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | — |
| France medium confidence | 8 1/4" | 6 5/16" | 8 1/4" | — | 6' 2 13/16" | 27 9/16" | 31 1/2"–39 3/8" | 39 3/8" | — | 4 5/16" | 17' 2 11/16" |
| Germany (DIN 18065) | 7 7/8" | 5 1/2" | 9 1/16" | 3/16" | 6' 6 3/4" | 31 1/2" | 35 7/16"–43 5/16" | 35 7/16" | 39 3/8" | 4 5/16" | — |
| Greece high confidence | 7 1/16" | 5 1/8" | 9 13/16" | — | 7' 2 5/8" | 35 7/16" | 35 7/16"–39 3/8" | 39 3/8" | — | 5 7/8" | 11' 9 3/4" |
| Hungary high confidence | 7 7/8" | — | 10 1/4" | — | 6' 6 3/4" | 31 1/2" | 35 7/16"–39 3/8" | 37 3/8" | — | 4 3/4" | 9' 10 1/8" |
| Iceland high confidence | 7 1/16" | 4 3/4" | 9 7/16" | — | 6' 10 11/16" | 35 7/16" | 31 1/2"–35 7/16" | 35 7/16" | — | 3 1/2" | 10' 9 15/16" |
| Ireland high confidence | 8 11/16" | — | 8 11/16" | — | 6' 6 3/4" | 31 1/2" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | 11' 6 9/16" |
| Italy medium confidence | 6 7/8" | — | 11 13/16" | — | 6' 10 11/16" | 31 1/2" | 35 7/16"–39 3/8" | 39 3/8" | — | 3 15/16" | — |
| Latvia high confidence | 7 1/16" | 4 3/4" | 9 7/16" | — | — | 35 7/16" | 35 7/16"–39 3/8" | 43 5/16" | — | 4 3/4" | — |
| Lithuania high confidence | 7 7/8" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 4 3/4" | 10' 1/2" |
| Luxembourg medium confidence | 6 11/16" | — | 9 13/16" | — | 7' 2 5/8" | 47 1/4" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | — |
| Malta medium confidence | 8 11/16" | — | 8 11/16" | — | 6' 6 3/4" | 35 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | 25' 11 13/16" |
| Moldova high confidence | 5 7/8" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 35 7/16"–39 3/8" | 47 1/4" | — | 3 15/16" | 8' 10 5/16" |
| Montenegro medium confidence | 7 1/16" | — | 11" | — | 7' 2 5/8" | 47 1/4" | 35 7/16"–39 3/8" | 43 5/16" | — | 3 15/16" | 7' 1 1/16" |
| Netherlands high confidence | 7 3/8" | — | 8 11/16" | — | 7' 6 9/16" | 31 1/2" | 31 1/2"–39 3/8" | 39 3/8" | — | 3 15/16" | 13' 1 1/2" |
| North Macedonia medium confidence | 7 1/16" | — | 11" | — | 6' 10 11/16" | 43 5/16" | 35 7/16"–39 3/8" | 39 3/8" | — | 3 15/16" | 10' 7 9/16" |
| Norway high confidence | 7 11/16" | — | 9 13/16" | — | 6' 6 3/4" | 31 1/2" | 27 9/16"–35 7/16" | 35 7/16" | — | 3 15/16" | 10' 9 15/16" |
| Poland high confidence | 7 1/2" | — | 9 13/16" | — | 6' 6 3/4" | 31 1/2" | 35 7/16"–39 3/8" | 35 7/16" | — | 4 3/4" | — |
| Portugal medium confidence | 7 5/8" | — | 9 13/16" | — | 7' 10 1/2" | 31 1/2" | 33 7/16"–35 7/16" | 43 5/16" | — | 3 9/16" | 7' 10 1/2" |
| Romania high confidence | 6 7/8" | — | 10 5/8" | — | 6' 6 3/4" | 37 3/8" | 35 7/16"–35 7/16" | 35 7/16" | — | 3 15/16" | — |
| Russia high confidence | 8 11/16" | 1 15/16" | 9 13/16" | — | 7' 2 5/8" | 41 5/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | 11' 6 9/16" |
| Serbia high confidence | 7 1/16" | — | 11" | — | 7' 2 5/8" | 47 1/4" | 35 7/16"–39 3/8" | 43 5/16" | — | 4 3/4" | 10' 1/2" |
| Slovakia high confidence | 7 7/8" | 5 7/8" | 8 1/4" | — | 6' 10 11/16" | 35 7/16" | 35 7/16"–47 1/4" | 39 3/8" | — | 4 3/4" | 10' 7 9/16" |
| Slovenia medium confidence | 7 1/2" | — | 9 13/16" | — | 6' 6 3/4" | 31 1/2" | 35 7/16"–39 3/8" | 39 3/8" | — | 4 3/4" | — |
| Spain high confidence | 7 7/8" | — | 8 11/16" | — | 6' 10 11/16" | 31 1/2" | 35 7/16"–43 5/16" | 35 7/16" | — | 3 15/16" | 10' 6" |
| Sweden high confidence | 7 7/8" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | — |
| Switzerland medium confidence | 7 1/2" | — | 10 1/4" | — | 6' 10 11/16" | 35 7/16" | 33 7/16"–35 7/16" | 39 3/8" | — | 4 3/4" | — |
| Turkey high confidence | 7 1/16" | — | 10 5/8" | — | 6' 10 11/16" | 47 1/4" | 35 7/16"–39 3/8" | 43 5/16" | — | 3 15/16" | 9' 10 1/8" |
| UK (Part K) | 8 11/16" | 5 7/8" | 8 11/16" | — | 6' 6 3/4" | — | 35 7/16"–39 3/8" | 35 7/16" | 23 5/8" | 3 15/16" | — |
| Ukraine medium confidence | 7 7/8" | — | 7 1/16" | — | — | 41 5/16" | 35 7/16"–39 3/8" | 47 1/4" | — | — | — |
| Asia-Pacific | |||||||||||
| Afghanistan low confidence | 7 11/16" | — | 10" | — | 6' 8" | 36" | 34"–38" | 36" | — | 4" | 12' |
| Australia (NCC) | 7 1/2" | 4 1/2" | 9 7/16" | 3/8" | 6' 6 3/4" | — | 34 1/16"–43 5/16" | 39 3/8" | 39 3/8" | 4 15/16" | — |
| Bangladesh medium confidence | 9 1/16" | — | 13" | — | 7' 1" | 44 1/8" | 33 7/8"–37 13/16" | 41 5/16" | — | 3 15/16" | 12' |
| China high confidence | 6 7/8" | — | 10 1/4" | — | 7' 2 5/8" | 43 5/16" | 35 7/16"–39 3/8" | 47 1/4" | — | 4 5/16" | 10' 4" |
| India medium confidence | 7 1/2" | — | 9 13/16" | — | 7' 2 5/8" | 35 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | 7' 5 3/4" |
| Indonesia low confidence | 7 7/8" | — | 11" | — | 6' 6 3/4" | 47 1/4" | 34 1/16"–38" | 39 3/8" | — | 3 15/16" | — |
| Japan high confidence | 9 1/16" | — | 5 7/8" | — | 6' 10 11/16" | 29 1/2" | 35 7/16"–39 3/8" | 43 5/16" | — | 4 5/16" | 13' 1 1/2" |
| Malaysia high confidence | 7 1/16" | — | 10 1/16" | — | 6' 6 3/4" | — | 32 1/2"–35 7/16" | 39 3/8" | — | — | 13' 11 5/16" |
| Myanmar high confidence | 8" | 4" | 10" | — | 7' | 36" | 36"–39 3/8" | 36" | — | 4" | — |
| Nepal high confidence | 7 1/2" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 35 7/16"–35 7/16" | 39 3/8" | — | — | — |
| Pakistan medium confidence | 7 1/16" | — | 9 1/16" | — | 6' 10 11/16" | 47 1/4" | 35 7/16"–39 3/8" | — | — | — | — |
| Philippines high confidence | 7 7/8" | — | 9 13/16" | — | 6' 6 3/4" | 29 1/2" | 31 1/2"–35 7/16" | 43 5/16" | — | — | 11' 9 3/4" |
| South Korea high confidence | 7 1/16" | — | 10 1/4" | — | 6' 10 11/16" | 47 1/4" | 33 7/16"–33 7/16" | 47 1/4" | — | 3 15/16" | 9' 10 1/8" |
| Thailand high confidence | 7 7/8" | — | 8 11/16" | — | 6' 2 13/16" | 31 1/2" | 35 7/16"–39 3/8" | — | — | — | 9' 10 1/8" |
| Uzbekistan medium confidence | 6 11/16" | 5 1/8" | 11" | — | — | 41 5/16" | 35 7/16"–39 3/8" | 35 7/16" | — | — | 10' 1/2" |
| Vietnam high confidence | 7 1/2" | 1 15/16" | 9 13/16" | — | 6' 6 3/4" | 27 9/16" | 35 7/16"–39 3/8" | 35 7/16" | — | 3 15/16" | — |
| Americas | |||||||||||
| Argentina high confidence | 7 1/16" | — | 9 1/16" | — | 6' 6 3/4" | 39 3/8" | 33 7/16"–39 3/8" | 33 7/16" | — | 4 3/4" | 12' 4 13/16" |
| Brazil medium confidence | 7 1/16" | 6 5/16" | 11" | — | 6' 10 11/16" | 47 1/4" | 27 9/16"–36 1/4" | 43 5/16" | — | 4 5/16" | 10' 6" |
| Canada (NBC) | 7 7/8" | 4 15/16" | 10 1/16" | 3/8" | 6' 4 3/4" | 33 7/8" | 34 1/16"–42 1/8" | 35 7/16" | 23 5/8" | 3 15/16" | 12' 1 11/16" |
| Colombia high confidence | 7 1/16" | 3 15/16" | 11" | — | 6' 6 3/4" | 29 1/2" | 27 9/16"–35 7/16" | — | — | — | 11' 5 13/16" |
| Mexico high confidence | 7 1/16" | 3 15/16" | 9 13/16" | — | — | 35 7/16" | 35 7/16"–39 3/8" | 35 7/16" | — | — | 8' 10 5/16" |
| Peru high confidence | 7 1/16" | — | 9 13/16" | — | 6' 10 11/16" | 35 7/16" | 33 7/16"–39 3/8" | 39 3/8" | — | 5 7/8" | 10' 1/2" |
| Venezuela medium confidence | 7 7/8" | 5 7/8" | 10 1/4" | — | — | 47 1/4" | 29 1/2"–35 7/16" | 35 7/16" | — | 5 7/8" | 7' 10 1/2" |
| Middle East | |||||||||||
| Iran medium confidence | 7 1/16" | 3 15/16" | 11" | — | 6' 8 11/16" | 43 5/16" | 33 7/16"–35 7/16" | 35 7/16" | — | 4 5/16" | 12' 1 11/16" |
| Iraq low confidence | 7 7/8" | — | 9 13/16" | — | — | — | 35 7/16"–39 3/8" | — | — | — | — |
| Saudi Arabia medium confidence | 7 7/8" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 34 1/16"–38" | 42" | — | 3 15/16" | 12' |
| Yemen low confidence | 7 7/8" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 34 1/16"–38" | 42" | — | 3 15/16" | 12' |
| Africa | |||||||||||
| Algeria low confidence | 6 5/16" | — | 12 5/8" | — | — | 31 1/2" | 35 7/16"–39 3/8" | 39 3/8" | — | 4 5/16" | — |
| Angola medium confidence | 7 5/8" | — | 9 13/16" | — | — | 31 1/2" | 35 7/16"–39 3/8" | — | — | — | — |
| DR Congo low confidence | 8 1/4" | 6 5/16" | 8 1/4" | — | 6' 2 13/16" | 27 9/16" | 35 7/16"–39 3/8" | 39 3/8" | — | 4 5/16" | — |
| Egypt high confidence | 6 11/16" | — | 10 5/8" | — | 6' 10 11/16" | 43 5/16" | 35 7/16"–47 1/4" | 35 7/16" | — | 5 7/8" | 7' 9 11/16" |
| Ethiopia low confidence | 7 7/8" | — | 9 13/16" | — | 7' 10 1/2" | — | 35 7/16"–39 3/8" | — | — | — | — |
| Ghana medium confidence | 7 1/2" | — | 9 13/16" | — | 6' 6 3/4" | 35 7/16" | 35 7/16"–39 3/8" | 39 3/8" | — | 3 15/16" | — |
| Kenya medium confidence | 7 1/2" | — | 9" | — | 6' 9" | 30" | 35 7/16"–39 3/8" | 33" | — | 5" | 10' |
| Morocco low confidence | 6 5/16" | — | 11" | — | — | 47 1/4" | 31 1/2"–39 3/8" | 35 7/16" | — | — | — |
| Mozambique medium confidence | 7 5/8" | — | 9 13/16" | — | — | 31 1/2" | 35 7/16"–39 3/8" | — | — | — | — |
| Nigeria high confidence | 7 1/16" | 3 15/16" | 11" | — | 6' 10 11/16" | 36" | 34"–38" | 43 5/16" | — | 5 7/8" | 9' 10 1/8" |
| South Africa medium confidence | 7 7/8" | — | 9 13/16" | — | 6' 10 11/16" | 29 1/2" | 33 7/16"–39 3/8" | 39 3/8" | — | 3 15/16" | 9' 10 1/8" |
| Sudan low confidence | 7 7/8" | — | 9 13/16" | — | — | — | 35 7/16"–39 3/8" | — | — | — | — |
| Tanzania low confidence | 7 1/2" | — | 9" | — | 6' 9" | 30" | 33"–39 3/8" | 33" | — | 5" | — |
| Uganda high confidence | 6 7/8" | — | 9 1/16" | — | 6' 10 11/16" | 35 7/16" | 33 1/16"–39 3/8" | 35 7/16" | — | 4 15/16" | 8' 7/16" |
IRC vs IBC at a glance
| Limit | IRC (residential) | IBC (commercial) |
|---|---|---|
| Max riser | 7¾″ | 7″ |
| Min tread/run | 10″ | 11″ |
| Min width | 36″ | 44″ |
| Guard height | 36″ | 42″ |
| Rise between landings | 12′-7″ | 12 ft |
Stair terminology
Frequently asked questions
How do I calculate the number of stairs I need?
Divide your total rise by an ideal riser height (about 7″), then round to the nearest whole number. That's your number of risers. Divide the total rise by that number to get the exact, equal riser height. Stairs Calc does this automatically and keeps every riser within code.
What is the ideal rise and run for stairs?
The most comfortable step is roughly a 7″ rise with an 11″ run — the "7‑11 rule." It satisfies the two classic comfort formulas (rise + run ≈ 17″–18″, and 2 × rise + run ≈ 24″–25″) and lands around a 32–33° angle.
How is stringer length calculated?
It's the hypotenuse of the staircase triangle: stringer = √(total rise² + total run²). For a 2921 mm rise and 4185 mm run that's about 16′‑9″. Buy your board 12″ longer to allow for the plumb and seat cuts.
How many treads are there compared to risers?
Always one fewer tread than risers, because the upper floor acts as the top step. A 16‑riser flight has 15 treads.
What's the maximum riser height allowed by code?
Under the US residential code (IRC) the maximum riser is 7¾″ and the minimum tread depth is 10″. Commercial buildings (IBC) are stricter: 7″ riser, 11″ tread. Stairs Calc checks this live and tells you the exact section.
What is the difference between standard and flush mount stringers?
With a standard mount the top tread sits one riser below the upper floor; with a flush mount the top tread is level with the upper floor. The practical difference is where the one‑tread‑thickness "drop" is removed — Stairs Calc adjusts the bottom step automatically so every finished riser ends up equal.
How much headroom do stairs need?
At least 6′8″ measured vertically from the nosing line, in both the IRC and IBC. The calculator shows the minimum floor‑opening length needed to achieve it.
Do my stairs need a handrail?
In a home (IRC), a handrail is required when there are four or more risers, mounted 34″–38″ above the nosings. A guard is required where the drop exceeds 30″.
Can I use this stair calculator in metric?
Yes. Toggle to millimeters at any time; every input and result, including fractions, converts instantly. UK users can also switch the code check to Approved Document K.
Is this stair calculator free?
Completely free, with no sign‑up. You can also copy a shareable link of your exact calculation, print a full‑scale stringer template, or download a PDF.
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Written by the Stairs Calc editorial team. Methodology and code references: see our methodology.
Built and maintained by builders, drafters and engineers who plan stairs for a living — every code limit is transcribed from the published standard and cited to its exact section.
Last reviewed 2026-06-20 against IRC 2021/2024
Stairs Calc gives accurate geometry and checks it against published building-code limits, but results are estimates for planning. Codes are adopted and amended locally and change over time. Always confirm dimensions against your local adopted code and a licensed professional before you build.