Stairs Calculator
Designing a staircase requires balancing comfort, safety, and available space. This calculator computes the number of steps, riser height, tread depth, and slope angle from the total rise and run of the staircase.
The comfort rule 2R + T (twice the riser height plus the tread depth) should fall between 60 and 65 cm for a comfortable staircase. Building codes typically require risers between 15–20 cm and treads no less than 22 cm.
How it works
Steps = Total Rise ÷ Target Riser Height (rounded). Actual Riser = Total Rise ÷ Steps. Tread Depth = Total Run ÷ (Steps − 1). Slope Angle = arctan(Total Rise ÷ Total Run). All dimensions in meters, converted to cm for display.
Use cases
- Designing a new staircase for a building project
- Verifying stair dimensions meet building code requirements
- Planning deck or porch stairs
- Calculating materials needed for stair construction
Frequently asked questions
How do I calculate how many steps a staircase needs?
Divide the total rise (floor-to-floor height) by your target riser height and round to the nearest whole number. Then divide the total rise by that number of steps to get the actual riser height. For example, a 2.80 m rise with a 17.5 cm target riser gives 16 steps with risers of exactly 17.5 cm.
What is a comfortable riser height for stairs?
Building codes typically require risers between 15 and 20 cm, and most people find heights around 17–18 cm the most comfortable. Risers above 20 cm make the staircase tiring and less safe, while very low risers waste horizontal space. Always check the result against the 2R + T comfort rule as well.
What is the 2R + T stair comfort rule?
The 2R + T rule (also known as Blondel's formula) states that twice the riser height plus the tread depth should fall between 60 and 65 cm, which matches the length of an average human stride. If the result is below 60 cm the stairs feel cramped and steep; above 65 cm they force an awkward, stretched gait.
What is the ideal angle for a staircase?
The slope angle is calculated as arctan(total rise ÷ total run). Staircases whose risers and treads satisfy the comfort rule usually end up between roughly 30 and 40 degrees. Steeper stairs save floor space but are harder to climb, while shallower stairs are more comfortable but need a longer run.
Why does the calculator divide the run by the number of steps minus one?
The last riser lands directly on the finished floor above, so a staircase always has one fewer tread than it has risers. That is why tread depth is computed as total run ÷ (steps − 1). Forgetting this detail is a common mistake that makes every tread slightly too shallow.