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Stair Calculator

Work out riser height, tread depth, stringer length, and stair angle from total rise, total run, and number of steps — in metric or imperial units.

Riser height
17.86 cm
Tread depth
28.57 cm
Stringer (diagonal) length
471.7 cm
Stair angle
32°
Comfort check (2 x riser + tread)
64.29 cm — within Blondel's comfortable range

How it works

This divides the total rise and total run evenly across the number of steps you enter: riser height = total rise ÷ steps, and tread depth = total run ÷ steps — the common simplified model most stair calculators use, treating each step as one equal riser-and-tread pair.

The stringer — the diagonal board a staircase's steps are actually built on — is the straight-line distance from the bottom of the rise/run to the top, found with the Pythagorean theorem: stringer = √(total rise² + total run²). The stair's angle from horizontal follows from the same triangle: angle = atan(total rise ÷ total run).

Riser height and tread depth are also checked against Blondel's step formula (1675), a long-standing architectural rule of thumb that a comfortable stride keeps 2 × riser height + 1 tread depth within roughly 24–25.5 inches (about 61–65 cm) — taller risers need shorter treads and vice versa to match a natural step length. Falling outside that range doesn't mean the stairs are unsafe, just that they may feel unusually steep or shallow to walk.

FAQ

What's the difference between total rise and total run?

Total rise is the vertical distance the staircase climbs — typically your floor-to-floor height. Total run is the horizontal distance the staircase occupies from its first step to its last, not counting any landing at the top. Both are needed to size the steps and the stringer correctly; rise alone (or run alone) isn't enough.

Why isn't there a single 'ideal' number of steps this calculator picks for me?

The right number of steps depends on your specific project — available headroom, local building code minimums and maximums for riser height, and personal preference all vary by situation, and none of those are facts this calculator can look up for you. Instead, try a few step counts and use the Blondel comfort check above to see which one lands in the comfortable range for your total rise and run.

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