Stair design tool
Stair Calculator
Work out risers, riser height, tread run, total run, stair angle and the diagonal cut line from one measurement — with a live section diagram and IRC or UK code checks. Free, no account needed.
Finished floor to finished floor.
7-7.5in is comfortable; risers are equalised.
Horizontal depth, nosing excluded.
Plumb from the nosing line to the ceiling above.
Landings, stringers & handrail
Half-landings or quarter-turns in this flight.
16in suits most treads; 12in for thin or composite.
Measured above the nosing line.
4in (100mm) sphere rule.
Sets the bottom stringer drop.
Your flight
15 risers × 7.33in
14 treads at 10.50in / 26.7cm · 36.8 degree pitch
- Riser height (equal)
- 7.33in / 18.6cm
- Tread run (going)
- 10.50in / 26.7cm
- Total run
- 147.00in / 373.4cm
- Cut line (diagonal)
- 183.60in / 466.3cm
- Stringer stock length
- 195.60in / 496.8cm (16.3ft)
- Pitch
- 36.8 degrees
- 2R + G
- 25.17in / 63.9cm
- Stringers
- 4 at 12.0in centres (65.2ft stock)
- Handrail length
- 207.60in / 527.3cm (17.3ft)
- Balusters
- 39 at 5.2in centres
Code & comfort checks
IRC (US) allows a maximum 7.75in riser. Every riser in a flight must match within 3/8in.
Minimum going is 10.00in. Shallow treads are the single biggest cause of descending falls.
Comfortable domestic flights sit between 30 and 37 degrees; 42 degrees is the absolute ceiling.
Two risers plus one going should land between 24in and 25in (600-640mm) for a natural stride.
IRC (US) expects at least 36.0in of clear width above the handrail height.
Minimum headroom is 80in measured plumb from the tread nosing line.
IRC wants a graspable handrail 34-38in above the nosing line, continuous for the full flight, and no gap that passes a 4in sphere.
Guidance only — confirm against your local building control before you cut or pour.
Compare riser counts
| Risers | Riser | Going | Run | Pitch |
|---|---|---|---|---|
| 14 | 7.86in | 10.50in | 11.4ft | 38.9° |
| 15 | 7.33in | 10.50in | 12.3ft | 36.8° |
| 16 | 6.88in | 10.50in | 13.1ft | 34.9° |
The highlighted row is your current flight. Nudging the riser count is usually the cheapest way to bring a steep or shallow stair back inside code.
Advanced layout
Mark-out schedule, framing deductions & take-off
Quick answer
How do you calculate a staircase?
Divide the total rise, measured finished floor to finished floor, by your target riser height and round to the nearest whole number to get the riser count. Divide the total rise by that count for an equal riser height. Treads are one fewer than risers when the top step is the upper floor. Multiply the tread run by the tread count for total run, and the pitch is the arctangent of rise over run. Check the result against 2R + G between 24in and 25in, a maximum 7 3/4in riser and a minimum 10in going.
- Risers = total rise divided by target riser height, rounded to a whole number.
- Riser height = total rise divided by the riser count, so every riser is equal.
- Treads = risers minus one when the top step is the finished upper floor.
- Total run = tread run multiplied by the number of treads.
- Pitch = atan(total rise / total run); keep it between 30 and 37 degrees.
- Comfort check: two risers plus one going should land between 24in and 25in.
The five numbers every stair calculation comes down to
A staircase is defined by total rise, riser count, riser height, tread run and total run. Everything else — pitch, diagonal cut line, stringer stock, headroom — falls out of those five. Measure the total rise from finished floor to finished floor, not from subfloor, because a 3/4in floor build-up at the top turns an equal flight into an uneven one and that is the single most common layout error.
- Measure total rise, finished surface to finished surface.
- Divide by a target riser of 7 to 7.5in and round to a whole number of risers.
- Divide the total rise by that riser count so every riser is identical.
- Choose a tread run of 10in or more, or fit the treads into the run you have.
- Check pitch, headroom and 2R + G before anything is cut.
| Total rise | Risers | Riser height | Treads (flush top) | Total run at 10.5in | Pitch |
|---|---|---|---|---|---|
| 96in / 2438mm | 13 | 7.38in | 12 | 126in | 37.3 deg |
| 104in / 2642mm | 14 | 7.43in | 13 | 136.5in | 37.3 deg |
| 110in / 2794mm | 15 | 7.33in | 14 | 147in | 36.8 deg |
| 120in / 3048mm | 16 | 7.50in | 15 | 157.5in | 37.3 deg |
| 132in / 3353mm | 18 | 7.33in | 17 | 178.5in | 36.5 deg |
Rise and run: what the codes actually allow
Codes set the envelope; comfort sets the target inside it. The IRC caps the riser at 7 3/4in and the tread at a 10in minimum, and allows no more than 3/8in variation between the tallest and shortest riser in a flight. UK Approved Document K works in pitch and going instead, allowing a maximum 42 degree pitch on private stairs with a minimum 220mm going. Switch the code selector in the calculator and the checks change with it.
Know your numbers in 30 seconds
Enter your step count, tread depth and riser height — the stair runner calculator gives you the exact length to order, in metres and feet, with waste included.
Open the stair runner calculatorThe 2R + G comfort rule
Two riser heights plus one going should add up to between 24in and 25in (600-640mm). It is an old rule from stride length and it still predicts how a flight feels better than any single dimension. A 7.5in riser with a 10in going gives 25in and walks well. A 7.75in riser with a 9in going gives 24.5in but fails the tread minimum, which is how steep, shallow flights end up feeling unsafe even though the arithmetic looks acceptable.
Free tools and the advanced layout
The calculator above is free and open — geometry, live section diagram, pitch, diagonal cut line and full code checks, with no account and no email. The advanced layout panel underneath is where the job actually gets built: a step-by-step mark-out schedule giving the height above the floor and run from the first riser for every tread, the bottom stringer drop, the top framing deduction, the run needed to clear headroom and a surface-area take-off. That panel needs a free account.
- Free, no account: risers, riser height, treads, going, total run, pitch, diagonal, code and comfort checks, diagram, copy to clipboard.
- Free account: step-by-step mark-out schedule for every tread.
- Free account: bottom stringer drop and top framing deduction.
- Free account: headroom clearance run and surface-area take-off.
- Riser portal: save the flight to a project, attach photos and client details, and turn it into a branded quote or invoice.
Equal risers are a code requirement, not a preference
Rounding the riser count and recalculating the height — rather than forcing a round 7in riser and absorbing the remainder in the last step — is what keeps a flight inside the 3/8in tolerance. The calculator always equalises for you.
From carcass to finish
Once the flight is set out, the same rise, going and nosing figures drive the soft finish. The advanced panel returns an approximate runner length so you can budget both trades at once, and the stair runner calculator on the home page refines it for landings, winders and pattern repeat. If you are cutting the carriages yourself, the stair stringer calculator adds notch geometry, throat depth and how many stringers the width needs.
Whatever you decide, get the numbers first: the stair runner calculator doubles as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length the first time.
Frequently asked questions
How do I calculate the number of stairs I need?
Measure the total rise from the finished lower floor to the finished upper floor, then divide by a comfortable riser height — 7 to 7.5in (175-190mm). Round to the nearest whole number and divide the total rise back by that number. A 110in rise divided by 7.25in gives 15.2, so 15 risers at 7.33in each. Never leave a remainder step; unequal risers fail inspection and cause trips.
What is the standard stair rise and run?
US residential practice under the IRC is a maximum 7 3/4in riser with a minimum 10in tread run, and most comfortable flights sit at roughly 7 1/4in rise with a 10 1/2in run. UK Approved Document K allows up to a 220mm rise with a 220mm minimum going on private stairs, with a maximum 42 degree pitch.
How do I calculate stair angle or pitch?
Pitch is the arctangent of total rise divided by total run. A 110in rise over a 147in run gives 36.8 degrees. Anything above 42 degrees is outside domestic code, and above 37 degrees starts to feel steep underfoot — lengthen the run or add a landing rather than steepen the flight.
Can this calculator fit stairs into a fixed opening?
Yes. Tick 'fit the flight into a fixed opening' and enter the horizontal space you have. The tool divides that run into equal treads for the riser count it worked out, then flags the going if it drops below the code minimum so you know when you genuinely need a landing or a winder.
How much headroom do stairs need?
The IRC requires 6ft 8in (80in) measured plumb from the tread nosing line; UK Document K asks for 2m, reduced to 1.9m at the centre of a loft stair. The calculator also returns the horizontal run the flight needs before the ceiling opening clears the nosing line, which is the figure most loft conversions get wrong.
Is the stair calculator free?
The geometry, diagram and code checks are free with no account. The advanced layout — the step-by-step mark-out schedule, framing deductions, headroom clearance and material take-off — needs a free account, and signed-in users get the same tool inside the Riser portal where flights can be saved to a project and quoted.
Does it work for deck and concrete stairs?
Yes. Choose deck for exterior steps and the layout allows for the bottom stringer drop and top framing deduction; choose concrete and you also get an estimated volume in cubic yards for the steps plus a 6in structural slab under the flight.