Stair Calculator
Riser count, exact riser height, tread run and stringer length for a straight run of stairs.
Stairs fail inspection for one reason above all others: inconsistent risers. The total rise is fixed by the building, so the number of risers you choose decides the height of every single step. Pick a target riser, round up to a whole number of risers, then divide again — that second division is the number you actually cut to.
The template is the stringer. Its length is the diagonal of the total rise and the total run, which is why the run shrinks by one tread: you count treads, not risers, along the horizontal. Cut one stringer, test-fit it, then use it as the pattern for the rest. Never cut all three from a calculated number alone.
How this calculator works
Every field is editable and the result updates as you type — nothing is submitted anywhere, all the maths runs in your browser. That matters for a number you are about to spend money on: you can see exactly which input moved the answer, and by how much.
What this calculation assumes
Assumes a straight run with no landing and a floor-to-floor rise measured finished-surface to finished-surface. Winders, landings, open risers and any stair with a change of direction need each run calculated separately.
Treat the result as an order-of-magnitude check rather than a final quantity. Product packaging changes, regional labour rates vary by a factor of two, and no calculator has seen your actual site.
Frequently asked questions
What is a comfortable riser height?
Seven to seven and a half inches suits most adults; six to seven inches feels easier on a main stair, and codes generally cap risers at 7.75 inches. The relationship that matters is riser plus tread: aim for roughly 17 to 18 inches combined, so a 7 inch riser pairs with a 10 or 11 inch tread.
How many stringers do I need?
Two for stairs up to 36 inches wide. Add a third at the centre for anything wider than about 36 inches, and use 2x12 stock — a 2x10 is not deep enough once the notch is cut out of it, and an over-notched stringer is a structural failure waiting to happen.
Do I need a landing?
Any stair rising more than about 12 feet needs an intermediate landing, and most codes require one where the total rise exceeds 147 inches. A landing also breaks a fall, so even on shorter runs it is worth adding if the stair serves a main floor.
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