Roofing & buildingFree calculator
Design a comfortable, safe staircase. Enter the total rise and your limits for riser height and tread depth to get the number of steps, exact riser height, total run and stringer length.
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How to measure
- Measure the total rise from the finished floor below to the finished floor above.
- Check your local building code for maximum riser height and minimum tread depth.
- Measure the width of the stairs to work out how many stringers you need.
The formula
Risers = total rise ÷ max riser height (round up) Riser height = total rise ÷ risers Treads = risers − 1 · Total run = treads × tread depth Comfort: 2 × riser + tread ≈ 24–25 in (60–65 cm)
Worked example
A total rise of 105 in with a 7.75 in maximum riser needs 14 risers of 7.5 in and 13 treads. With 10 in treads the total run is 130 in and the comfort check is 25 in.
Tips before you buy
- Every riser in a flight must be the same height. Small differences cause trips.
- US codes typically allow a maximum riser of 7¾ in and a minimum tread of 10 in.
- UK rules allow a maximum rise of 220 mm for private stairs; check local rules everywhere.
Frequently asked questions
What is a comfortable riser height?
About 7–7.5 in (17–19 cm) with a tread of 10–11 in (25–28 cm).
How many stringers do I need?
Three for stairs up to 36 in (90 cm) wide, and one more for every extra 16 in (40 cm).
What is the 2R + G rule?
Twice the riser plus the going (tread depth) should be about 24–25 in (600–650 mm) for a natural stride.
Results are estimates for planning only. Always check quantities with your supplier before you buy.