How to use this calculator
- Measure the total rise, from the finished lower floor to the finished upper floor.
- Enter the maximum riser height allowed (7¾ in under the US IRC; many countries allow 18–22 cm).
- Enter the tread depth (run per step, excluding nosing).
Formula
The number of risers is the total rise divided by the maximum riser height, rounded up, so every step is the same height. There is always one fewer tread than risers when the top step is the upper floor.
Risers = ⌈total rise ÷ max riser⌉
Riser height = total rise ÷ risers
Total run = (risers − 1) × tread
Stringer ≈ √(rise² + run²)
Comfort: 2 × riser + tread ≈ 24–25 in (61–64 cm)
Example
- Total rise 108 in, max riser 7.75 in → 108 / 7.75 = 13.9 → 14 risers.
- Riser height = 108 / 14 = 7.71 in; 13 treads × 10.5 in = 136.5 in total run.
- Stringer ≈ √(108² + 136.5²) ≈ 174 in.
Frequently asked questions
What are the US code limits?
The International Residential Code (R311.7) limits risers to 7¾ in and requires treads of at least 10 in, with a maximum 3/8 in variation between steps. Local codes may differ.
What is the 2R + T rule?
A long-standing comfort guideline: twice the riser height plus the tread depth should be about 24–25 in (610–635 mm), matching a typical stride.
Does the stringer length include cuts?
No. It's the diagonal length along the stair; buy stringer stock longer to allow for the top and bottom cuts.