Stair Rise & Run Calculator
Work out riser height, tread run, total run, stringer length and stair angle from your total rise, with IRC, IBC and UK code checks.
Enter your total rise (finished floor to finished floor) — the stair layout updates as you type.
- Risers
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- Riser height
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- Treads
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- Total run
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- Stringer length
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- Stair angle
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- Tread board width
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- 2 × riser + run
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Code & comfort checks
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Rule-of-thumb reference only. Always confirm the riser, tread, headroom and handrail rules with your local building authority or inspector before you cut a stringer.
Nearby riser counts
| Risers | Riser height | Total run | Angle | Riser OK? |
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How it works
A staircase is laid out from one measurement: the total rise, the vertical
distance from finished floor to finished floor. Divide it by your target riser height and
round up to a whole number to get the number of risers — rounding up keeps
every step at or below your target height; the exact riser height
is then total rise ÷ risers, so every step is identical. A straight flight has
one fewer tread than riser, so total run = (risers − 1) × tread run. The
stringer is the hypotenuse of that triangle: √(rise² + run²), and the pitch is
atan(rise ÷ run) in degrees.
The tread run entered here is the going — the horizontal distance from one nosing to the
next — which is what building codes measure as tread depth. Nosing overhang is added on top
of it only to size the tread board, never to the total run. The checks compare your layout
against IRC 2021 residential limits (riser ≤ 7¾ in, tread ≥ 10 in), IBC limits for public
stairs (riser ≤ 7 in, tread ≥ 11 in) or UK Approved Document K for private stairs (rise ≤
220 mm, going ≥ 220 mm, pitch ≤ 42°), plus the classic comfort rule
2 × riser + run = 24–25 in (Blondel's formula, 60–65 cm).
Everything is arithmetic done in your browser with plain JavaScript — no measurements are uploaded, no sign-up, no ads.
Frequently asked questions
How do I calculate stair rise and run?
Measure the total rise from finished floor to finished floor, divide it by your target riser height (about 7 in / 17.5 cm) and round to a whole number — that is your riser count. The exact riser height is total rise ÷ risers, so every step is identical. A straight flight has one fewer tread than riser, so the total run is (risers − 1) × tread run. Example: a 108 in rise gives 16 risers of 6.75 in, 15 treads and, at a 10.5 in going, a total run of 157.5 in.
What is the maximum riser height and minimum tread depth?
Under the 2021 IRC for US homes, risers may be no more than 7¾ in (196 mm) and treads no less than 10 in (254 mm) measured nosing to nosing, with no more than 3/8 in variation between steps. The IBC is stricter for public stairs: 7 in maximum riser, 11 in minimum tread. UK Approved Document K allows a rise up to 220 mm and a going of at least 220 mm for private stairs, with a pitch no steeper than 42°. The calculator flags your layout against whichever set you pick, but your local authority has the final say.
How long does the stair stringer need to be?
The stringer is the hypotenuse of the rise-and-run triangle: √(total rise² + total run²). For a 108 in rise and a 157.5 in run that is √(11,664 + 24,806.25) ≈ 190.97 in, or about 15 ft 11 in — so you would buy a 16 ft board and allow extra for the plumb cut at the top and the seat cut at the bottom. The calculator also gives the pitch, atan(rise ÷ run), which is 34.4° for that flight.