What the animation shows
The animation and the step-by-step video above use your numbers. Here is the same walkthrough written out for the default example.
What you enter
- Total rise: 36 in.
- Maximum riser height: 7.75 in. 7¾ in is the IRC residential maximum. Some jurisdictions differ.
- Tread depth (run per step): 10.5 in.
- Stair width: 3 ft.
- Maximum stringer spacing: 16 in.
What happens, step by step
- The stringer splits 36 in into 5 equal risers, none over 7 3/4 in.
- Treads go on one per step; the deck is the top step, so 4 treads.
- The stringer runs 55.32 in along the slope at 34.4 °.
- 4 stringers span the 3 ft width, at most 16 in apart.
The answer: number of risers is 5.
How it’s calculated
- Risers = total rise ÷ max riser, rounded up
- Riser height = total rise ÷ risers
- Treads = risers − 1 (top step is the deck surface)
- Stringer = √(rise² + run²)
Worked example
36 in total rise, 7¾ in max riser, 10½ in treads, 3 ft wide.
Inputs
- Total rise
- 36 in
- Maximum riser height
- 7.75 in
- Tread depth (run per step)
- 10.5 in
- Stair width
- 3 ft
- Maximum stringer spacing
- 16 in
Results
- Number of risers
- 5
- Riser height
- 7.2 in
- Number of treads
- 4
- Total run
- 42 in
- Stringer length (minimum)
- 55.32 in
- Stringers
- 4
- Stair angle
- 34.4 °
Assumptions and limits
- The top step is the deck or floor surface, so there is one fewer tread than risers.
- All risers are equal (a code requirement, typically within ⅜ in).
Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.
Questions
How many steps for a 36 inch rise?
36 ÷ 7.75 = 4.6, so 5 risers of 7.2 in each, with 4 treads.
What are the IRC stair limits?
The IRC sets a maximum riser of 7¾ in and a minimum tread of 10 in for residential stairs. Your jurisdiction may amend these.