Your privacy is protected! No data is transmitted or stored.
Frequently Asked Questions
Divide the total rise — the finished floor to finished floor height — by a comfortable riser height, then round to a whole number. That gives your riser count. Dividing the total rise by that count gives the exact riser height, which is what keeps every step identical. A flight always has one more riser than tread, because the top riser lands on the upper floor rather than on a tread.
Riser height = total rise divided by the number of risers. Total run = number of treads multiplied by the tread depth, where treads are always one fewer than risers. Stringer length is the diagonal, so it is the square root of the total rise squared plus the total run squared. The stair angle is the arctangent of the total rise divided by the total run. Our guide on how to calculate stairs works the whole formula through with a example, and compares what the same rise looks like under four different building codes.
Because the stringer sits directly on the lower floor, but a tread board then sits on top of the first notch. If every notch were cut the same, that first step would end up one tread thickness taller than the rest — uncomfortable to walk on and a code violation. The fix is to cut the bottom of the stringer down by the tread thickness, which carpenters call dropping the stringer. If finished flooring still has to go down at the bottom, subtract that thickness from the drop.
It depends on the code you are building to. US residential work under the IRC allows a maximum riser of 7 and three quarter inches with a minimum tread of 10 inches when there is a nosing. US commercial work under the IBC is tighter at 7 inches maximum riser and 11 inches minimum tread. UK Part K allows a rise up to 220 mm with a going of at least 220 mm and a pitch no steeper than 42 degrees. Australia and New Zealand under the NCC require risers between 115 and 190 mm and goings between 240 and 355 mm.
It is the comfort check that ties riser height and tread depth together, because a tall riser needs a shallower tread and the other way round. Twice the riser plus the going should land between 550 and 700 mm, which is the range written into UK and Australian codes. In inches the same idea is usually quoted as twice the riser plus the tread falling between 24 and 25 inches.
Long enough that anyone walking under the upper floor still has headroom. Take the required headroom, add the thickness of the upper floor structure, divide by the riser height to find how many risers the stair must drop, then multiply by the tread depth. Most codes ask for at least 6 feet 8 inches, or 2 metres, of headroom measured vertically from the tread nosings.
No. The calculation is geometry that runs inside your browser. Nothing is uploaded, stored or logged, and the tool keeps working if you go offline after the page has loaded.