Stair calculator
This stair calculator turns the total rise of a staircase into the number of steps, riser height, tread depth, total run and pitch angle. A total rise of 108 in gives 16 risers of 6.75 in and 15 treads of about 11.1 in – checked against the US building code (IRC), UK Approved Document K or the German DIN 18065.
Example: Total rise (finished floor to finished floor) 108 · Available run (0 = free) 0 · Unit: Inches · Code to check against: US – International Residential Code → Result: 16 risers of 6.75 in, 15 treads of 11.11 in. Source: Wikipedia – Stairs: building codes, 2 × riser + tread, UK Approved Document K (rise 150–220 mm, going 220–300 mm, pitch ≤ 42°). Updated: .
How it is calculated
How to calculate stairs
The total rise is divided into a whole number of risers close to 7 in (17.5 cm). The tread then follows from the step rule 2 × riser + tread ≈ 25 in (63 cm). A flight with n risers has n − 1 treads, because the top “step” is the upper floor itself.
Example
Total rise 108 in: 108 ÷ 16 = 6.75 in riser, tread 24.6 − 2 × 6.75 ≈ 11.1 in, total run 15 × 11.1 in ≈ 167 in, pitch about 31 degrees. The ratio 17/29 (riser to tread) is often quoted as the comfortable ideal.
What the codes say
- US (IRC R311.7.5): riser at most 7¾ in, tread at least 10 in.
- UK (Approved Document K, private stairs): rise 150–220 mm, going 220–300 mm, 2R + G between 550 and 700 mm, pitch at most 42°.
- Germany (DIN 18065): riser up to 19 cm, tread at least 26 cm, step rule 63 cm ± 3 cm.
Honest limits
This calculator plans one straight flight without landings or winders. Your local building authority decides which rules apply, and headroom, handrails, guards and stair width are not covered here. Treat the result as a planning value and measure the real floor-to-floor height on site.
Frequently asked questions
How do I calculate stairs rise and run?
Divide the total rise by about 7 in (17.5 cm) and round to whole steps. Riser = rise ÷ steps; the tread follows from 2 × riser + tread ≈ 25 in.
What is the maximum riser height in the US?
The IRC allows up to 7¾ in for residential stairs, with a minimum tread depth of 10 in. Local codes can be stricter.
How many steps do I need for a 108 inch rise?
16 risers of 6.75 in. There are only 15 treads, because the top step is the upper floor.
What is the stair rule 2R + G?
Twice the rise plus the going should be about 550–700 mm in the UK and roughly 625 mm (24.6 in) as an ideal step length.
How long will my staircase be?
Total run = number of treads × tread depth. With 15 treads of 11.1 in that is about 167 in (14 ft).
Sources and legal basis
- Wikipedia – Stairs: building codes, 2 × riser + tread, UK Approved Document K (rise 150–220 mm, going 220–300 mm, pitch ≤ 42°)
- International Residential Code 2024, R311.7.5 – maximum riser height 7¾ in, minimum tread depth 10 in
As of: · Editorial policy
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