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StepCalc

Stair calculator

Floor-to-floor height in, full stair out — risers, treads, run, pitch, stringer and a code check.

Units
Finished floor thicknesses

If your total rise was measured on subfloor, put the finishes here. Different thicknesses top and bottom change the first and last riser — which is how a stair ends up failing the uniformity rule after the flooring goes down.

Turn this into a full project — drawings, stringer cuts, floor opening and a cut list. Save it with a free account.

How this is worked out

Two steps in section. The pitch line touches each nosing — headroom and pitch are both measured from it, not from the tread surface.treadnosingriser (the board)goingrisepitch line
Two steps in section. The pitch line touches each nosing — headroom and pitch are both measured from it, not from the tread surface.

The riser count is an integer by nature — you cannot build 14.3 risers — so the count is settled first and the riser height falls out of it: 

risers    = round(total rise / target riser)
riser     = total rise / risers
treads    = risers − 1          (when the top step is the upper floor)
total run = treads × going
pitch     = atan(riser / going)
stringer  = √(total rise² + total run²)

That order matters. Fixing the riser height first and letting the count come out fractional is what produces a stair with one odd riser at the top, and an odd riser is the thing that trips people — research on stair falls consistently finds uniformity matters more than height.

Where no going is given, it is derived from Blondel's rule: 2R + G = 630mm, the middle of the comfortable band, so the tread suits the riser height actually arrived at rather than a fixed guess.

Before you cut

Check the floor opening for headroom, and read the common mistakes — particularly the stringer drop at the bottom cut, which catches people who have built stairs for years.