Measures · Staircase
Stair sizing with the Blondel formula FREE
Work out riser, tread and number of steps from the floor-to-floor height. Below the result you find the formula and the standard.
Indicative pre-sizing. It does not replace a structural calculation signed by a licensed engineer. For seismic zones with agS (design ground acceleration) > 0.15g, long spans or use classes III/IV → talk to a structural engineer.
Pick a calculation from the list to start.
Formula, example and standard
2a + p = 62 ÷ 64 cm (Blondel formula)
Example with the starting values (Floor-to-floor height: 2.7 m): 16 risers of 16.9 cm · tread 28-30 cm. Tread from Blondel: 30.3-32.3 cm · typical residential 28-30 cm.
- Blondel formula: 2·riser (a) + tread (p) = 62 ÷ 64 cm (standard human stride).
- Residential: riser 16-18 cm · tread 28-32 cm.
- Public stairs / escape use: tread ≥ 30 cm, riser ≤ 17 cm (DM 236/89, the Italian accessibility decree).
Source: DM 236/89 · handbooks · biblus.acca.it
Indicative pre-sizing: it does not replace a calculation signed by a licensed engineer.
The other calculations
Timber beamSteel IPE beamReinforced concrete beamReinforced concrete columnSteel columnTimber columnRC cantilever / balconyLintelClay block and concrete slabTimber floorPredalles slabLoad-bearing brick wallPartition wallMinimum room heightWindow-to-floor ratioEscape route widthNumber of toiletsNTC imposed loadsExternal insulationVentilated crawl spaceRoof pitch