Stair Calculator

Enter the floor-to-floor rise for a straight stair. Get equal risers, treads, total run and stringer length.

Worked example

Total rise 2600 mm, target riser 178 mm: 2600 / 178 = 14.6, so 15 risers. Actual riser height = 2600 / 15 = 173.3 mm. Treads = 15 - 1 = 14. Total run = 14 x 279 mm = 3906 mm (3.91 m). Stringer pitch-line length = sqrt(2600² + 3906²) = 4692 mm (4.69 m); buy stringer stock longer to allow for cuts.

How it works

Risers = total rise / target riser height, rounded to a whole number, then the actual riser height = total rise / risers so every step is equal. Treads = risers - 1, because the top tread is the upper floor. Total run = treads x tread run. Stringer length is the hypotenuse of total rise and total run. Ontario residential guidance ranges are roughly 125 to 200 mm for riser height and 255 to 355 mm for tread run, shown as guidance only: verify your local building code before building.

FAQ

Why is the actual riser height different from the target?

Steps must all be the same height, and the riser count must be a whole number. The calculator picks the count closest to your target, then divides the rise evenly so no step is taller or shorter than the others.

What if the riser comes out over 200 mm?

Add one more riser by lowering the target riser height. A riser that is too tall feels steep and may fail a code inspection.

Estimates only. This calculator gives planning estimates, not professional advice. Stair dimensions are regulated: confirm riser, run, headroom and handrail requirements with your local building department.