A staircase is set by one fixed number — the total rise from one finished floor to the next — and the trick is dividing it into steps that feel natural to climb. You choose how many risers to split it into so each one lands near a comfortable height, then the going (how deep each tread is) sets the total run and the slope. A simple comfort rule, twice the riser plus the going, keeps the whole flight matched to a human stride, and the diagonal stringer falls straight out of the rise and run.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: Blondel 2R+G comfort rule and standard stair geometry.
The staircase equations
Rounding the riser count to a whole number is essential — every riser in a flight must be identical, or the change in rhythm becomes a trip hazard. The number of treads is one fewer than the risers because the top "step" is the landing itself. The going sets both comfort and the floor space the stair consumes: deeper treads are easier to walk but eat more length.
Worked example — a domestic staircase
Scenario: A floor-to-floor rise of 2,700 mm, targeting a 175 mm riser and a 280 mm going.
Fifteen risers of exactly 180 mm climb the 2,700 mm rise, with fourteen 280 mm treads spanning 3,920 mm of floor. The stringer board needs to be about 4,760 mm long before end cuts. The comfort check gives 2×180 + 280 = 640 mm, right in the ideal band, and the stair sits at about 33° — a comfortable, code-friendly domestic slope.
Frequently Asked Questions
Divide total rise by a target riser (~175 mm) and round. 2700 ÷ 175 ≈ 15 risers → exact riser 180 mm. Treads = risers − 1.
Riser ~150–200 mm, going ~250–300 mm. Keep 2×riser + going between 600 and 660 mm for a natural stride.
Blondel's comfort rule: 2 × riser + going ≈ 600–640 mm. A 180 mm riser + 280 mm going = 640 mm.
It's the hypotenuse: √(total rise² + total run²). A 2700 rise + 3920 run ≈ 4760 mm. Add extra for connections.
~30–37° for comfort. angle = atan(riser/going); 180/280 ≈ 33°. Above ~42° is steep and tiring.