Staircase Calculator

How it is calculated

All three inputs are in centimetres. The number of risers is the total rise divided by your target riser height and rounded up: risers = ceil(rise / target riser), never fewer than 1. The real riser height is then actual = rise / risers, so it is equal to or slightly lower than your target. A staircase has one tread fewer than risers, because the upper floor is the last step: treads = risers − 1. The total run is run = treads × tread depth, and the stringer is the diagonal of the right triangle with legs rise and run: stringer = √(rise² + run²). The tool rejects a target riser below 5 cm or above 30 cm and a tread deeper than 100 cm, showing no result. Inside those limits it does not check headroom, building regulations or comfort rules, so compare the numbers with your local requirements.

Common mistakes

• Entering the rise in metres or millimetres. The field is in centimetres: 2.8 m must be typed as 280, and 2800 would give 156 risers and a 4,780.76 cm stringer.
• Typing a riser or tread that breaks the limits: a riser under 5 cm or over 30 cm, or a tread over 100 cm, shows no result, so a riser in inches or millimetres is usually caught.
• Expecting the riser height to equal the target. The count is rounded up, so the real riser (17.50 cm here) is lower than the 18 cm you typed, and the real value is the one to cut to.
• Counting 16 treads because there are 16 risers. There are 15 treads, since the top floor acts as the last step; the run uses 15.
• Measuring the rise from the unfinished floor, or ordering board exactly as long as the stringer figure. Total rise is finished floor to finished floor, and the stringer figure is only the diagonal, so allow extra for cut ends and connections.