The height between floors decides everything: the number of risers, their height, the depth of the treads and how much floor the staircase takes. For 280 cm floor to floor and a target riser of 17.5 cm, you get 16 risers of 17.5 cm; Blondel’s rule (2 risers + 1 tread = 63 cm) gives treads of 28 cm, a run of 4.2 m and a pitch of 32°. Type the total rise and your preferences in centimeters, millimeters or inches; the calculator divides the height evenly and checks comfort and the US residential code.
Metric: risers of about 17.5 cm, stride 63 cm
| Floor to floor | Risers | Riser | Tread | Run | Pitch |
|---|---|---|---|---|---|
| 250 cm | 14 | 17.9 cm | 27.3 cm | 3.55 m | 33.2° |
| 260 cm | 15 | 17.3 cm | 28.3 cm | 3.97 m | 31.5° |
| 270 cm | 15 | 18.0 cm | 27.0 cm | 3.78 m | 33.7° |
| 280 cm | 16 | 17.5 cm | 28.0 cm | 4.20 m | 32.0° |
| 290 cm | 17 | 17.1 cm | 28.9 cm | 4.62 m | 30.6° |
| 300 cm | 17 | 17.6 cm | 27.7 cm | 4.43 m | 32.5° |
US: risers of about 7¼ in, stride 25 in
| Floor to floor | Risers | Riser | Tread | Run |
|---|---|---|---|---|
| 96 in (8 ft) | 13 | 7.38 in | 10.23 in | 10.2 ft |
| 102 in (8½ ft) | 14 | 7.29 in | 10.43 in | 11.3 ft |
| 108 in (9 ft) | 15 | 7.20 in | 10.60 in | 12.4 ft |
| 114 in (9½ ft) | 16 | 7.13 in | 10.75 in | 13.4 ft |
| 120 in (10 ft) | 17 | 7.06 in | 10.88 in | 14.5 ft |
Every row meets the IRC limits (riser up to 7¾ in, tread at least 10 in).
Comfort in one number
Risers of 16–18 cm (6¼–7 in) feel natural indoors; up to about 20 cm is acceptable for a loft or a cellar, not for the main stairs. If the floor space is short, a steeper stair is tempting, but each centimeter of riser takes two centimeters off the tread under Blondel’s rule. Measure from finished floor to finished floor, including the flooring still to come: a 2 cm floor laid later changes the top or bottom riser.
Headroom, handrails, landings and widths also have rules where you live; check them before you cut a stringer. The calculator works offline in the workshop.
Frequently asked questions
How do I work out the number of steps?
Divide the floor-to-floor height by the riser height you want and round to a whole number; then divide the height by that number for the real riser. 280 cm ÷ 17.5 cm = 16 risers of exactly 17.5 cm.
What is Blondel's rule?
Two risers plus one tread should be about 63 cm (60–65 cm, roughly 24–25½ in): the length of a comfortable step. It goes back to the French architect François Blondel in 1675. With 17.5 cm risers, the tread is 63 − 35 = 28 cm.
Why is there one tread fewer than risers?
The last riser lands on the upper floor itself, which acts as the top tread. 16 risers mean 15 treads.
What are the US code limits for stairs?
For homes, the International Residential Code allows a riser of at most 7¾ in (19.7 cm) and asks for a tread of at least 10 in (25.4 cm). Many US states and cities adopt the IRC with their own changes, and other countries have their own rules.
How much floor space does a staircase take?
The total run: treads × tread depth. 15 treads of 28 cm take 4.2 m in plan, plus the landings at the top and the bottom.
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