Stair Calculator
Work out riser height, tread depth, total run and stringer length from a total rise, and check the result against US, UK and Australian stair code limits.
Code checks
- Riser height within limit — 7.20 in vs max 7.75 in passes
- Tread depth / going within limit — 10.00 in vs min 10.00 in passes
- 2 × riser + tread in comfort range — 24.40 in vs 24.00–25.00 in passes
- Pitch within limit — 37.6° vs max 42° passes
Risers = total rise ÷ target riser, rounded to a whole number, and every riser is then made exactly equal — codes allow only about 3⁄8 in (10 mm) of variation between the tallest and shortest riser. A flight that lands flush with the upper floor has one fewer tread than riser, so total run = (risers − 1) × going, and the stringer is √(rise² + run²). Measure the total rise to the finished floor level on both storeys, and remember that flooring thickness changes it. The presets show headline limits only, not the whole of any code — handrails, headroom, landings and nosing rules still apply, and building control has the final say. Estimates only.
What is the Stair Calculator?
The ByteTools Stair Calculator turns a total rise into a buildable flight. Enter the finished-floor-to-finished-floor height and your target riser, and it divides the rise into equal risers, gives the exact riser height, the number of treads, the total run, the stringer length by Pythagoras and the pitch in degrees.
- Equal risers calculated from any total rise
- Total run, stringer length and pitch angle
- 2R + T and R + T comfort rules shown alongside
- Code presets for IRC, IBC, UK Part K and Australia/NZ
- Pass or warning shown for every check
- Imperial and metric, calculated entirely in your browser
How to use the Stair Calculator
- 1
Choose imperial or metric and enter the total rise from finished floor to finished floor.
- 2
Enter your target riser height and the tread depth or going you plan to use.
- 3
Select the code preset that matches where you are building.
- 4
Read the riser count, exact riser height, total run and stringer length.
- 5
Check the four code checks and adjust the target riser or tread until they pass.
About the Stair Calculator
The ByteTools Stair Calculator turns a total rise into a buildable flight. Enter the finished-floor-to-finished-floor height and your target riser, and it divides the rise into equal risers, gives the exact riser height, the number of treads, the total run, the stringer length by Pythagoras and the pitch in degrees.
It then checks the design against the headline limits of a code preset — US residential (IRC), US commercial (IBC), UK Approved Document K, or typical Australian and New Zealand figures — covering maximum riser, minimum tread or going, the 2R + T comfort range and maximum pitch, with each check shown as a pass or a warning.
Everything runs locally in your browser with nothing uploaded. The presets are headline figures only, not the whole of any code: handrails, headroom, landings and nosings all have their own rules, and your local building control has the final say.
Frequently asked questions
What is the 7-11 rule for stairs?
It is the classic comfortable stair: a 7-inch riser with an 11-inch tread. That gives 2R + T = 25 inches, at the top of the 24-to-25-inch comfort range, and a pitch of about 32 degrees. It sits comfortably inside US residential limits of a 7¾-inch maximum riser and 10-inch minimum tread.
How do I calculate the number of stairs I need?
Divide the total rise by your target riser height and round to a whole number, then divide the total rise by that count to get the exact riser. A 108-inch rise with a 7-inch target gives 15.43, so 15 risers of 7.2 inches each.
Why is the number of treads one less than the number of risers?
The top riser lands on the upper floor, and that floor surface is the last tread. So a flight ending flush with an upper storey always has one fewer tread than riser, and the total run is (risers − 1) × the going.
How do I calculate stair stringer length?
It is the hypotenuse of the total rise and the total run: √(rise² + run²). A 108-inch rise with a 140-inch run gives a stringer of about 176.8 inches, or 14 ft 9 in. Order stock longer than that to allow for the cuts at each end.
Do all risers have to be the same height?
Effectively yes. Codes allow only about ⅜ of an inch (10 mm) of variation between the tallest and shortest riser in a flight, because an uneven step is a trip hazard people do not see. Always divide the total rise into exactly equal parts.
Are the code limits in this tool authoritative?
No. They are the commonly published headline figures for each jurisdiction and editions change. Handrails, headroom, landings, nosing projection and winder geometry are not modelled at all. Use this to sketch a workable flight, then confirm against the code adopted locally.
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