The stair calculator automatically determines the number of steps, actual riser height, tread depth, total run, angle, and stringer length based on the total floor height and desired step dimensions. It also checks design compliance using the Blondel formula (2R+T) and building code standards.
Calculate stair steps and dimensions based on floor height for comfortable and code-compliant home stairs.
Calculate step dimensions and total length in limited space to check feasibility for attic access.
Design garden or porch steps with proper dimensions for safety and slip resistance.
Estimate lumber requirements from stringer length and step count for purchasing stair materials.
The Blondel formula (2R+T=63±2cm) was proposed by French architect François Blondel in the 17th century and remains the golden rule for stair design. R is the riser height, T is the tread depth. The formula is based on the natural rhythm of human stride. The stringer length is calculated using the Pythagorean theorem: L=√(H²+R²), where H is total height and R is total horizontal run.
For residential stairs, the ideal riser height is typically 16-19cm (6.3-7.5 inches). Public buildings recommend 15-17cm. A comfortable riser height is about 17-18cm.
Residential stair tread depth should be at least 25cm (10 inches), public buildings at least 28cm. Deeper treads are more comfortable but increase total stair length.
The 2R+T rule (R=riser height, T=tread depth) is the classic stair comfort formula. The ideal value is 60-65cm. For example, riser 18cm + tread 28cm gives 2R+T=64cm, meeting the comfort standard.
A comfortable stair angle is 30-35 degrees. Residential stairs should not exceed 42 degrees, public buildings 38 degrees. Steeper angles are difficult and unsafe to climb.