Designing a comfortable staircase
Start from the total floor-to-floor height. Dividing it by a comfortable riser height rarely gives a whole number, so you round to the nearest whole number of risers and then recalculate the exact riser height so every step is identical — uneven steps are a trip hazard. The number of treads is always one less than the number of risers, because the top landing isn't a tread. The stringer is the sloped board that carries the steps, and its length is the diagonal across the total rise and total run.
Frequently asked questions
What's a comfortable riser and tread?
A riser of about 150–190 mm (6–7.5 in) with a tread of 250–300 mm (10–12 in) suits most homes. Many codes want two risers plus one tread to fall around 550–700 mm.
Why is there one fewer tread than risers?
The final riser lands on the upper floor, which acts as the last "step," so you don't need a separate tread there.
Is the stringer length exact?
It's the straight diagonal for the rise and run. Allow extra for the cut at the top and bottom and for how the stringer meets the floor and landing.