New build, attic conversion or garden stairs: the dimensions decide whether a staircase is comfortable or treacherous. The Staircase Calculator uses the proven step formula and checks the result against DIN 18065 – this tutorial explains the calculation path.
The step formula
2 × riser + tread = 59 to 65 cm, ideally 63 cm – the average human stride length. When climbing, each unit of height 'consumes' twice as much stride length as a unit of run; that is exactly what the formula captures. Added to this are the DIN 18065 limits for residential buildings: riser 14–20 cm, tread at least 23 cm.
Step by step
- Measure the floor height: from finished floor to finished floor – not the structural slab!
- Enter the run length (optional): if space is limited, the calculator distributes it across the treads
- Specify the riser count (optional): otherwise the calculator chooses it targeting ~18 cm riser
- Read the check: on rule violations the calculator proposes concrete alternatives
The textbook example
Floor height 280 cm: 16 risers of 17.5 cm, tread 63 − 35 = 28 cm. Since the top riser ends at floor level, 15 treads are needed and 15 × 28 = 420 cm run length at 32° pitch – the classic comfortable residential staircase. If space is tight, the basement example (250 cm height over 250 cm length) shows how the calculator reacts: tread too narrow, step formula violated – with the suggestion to change the number of steps.
What else counts
Besides riser and tread, the trade literature knows the comfort rule (tread − riser = 12 cm) and the safety rule (tread + riser = 46 cm) – only the 17/29 combination satisfies all three exactly; real staircases are always a compromise. Building law adds: usable flight width at least 80 cm, headroom 200 cm, intermediate landing from 18 risers, and for winder stairs the step formula applies along the walking line. For stairs requiring permits, the final design belongs in the hands of a carpenter or architect.
