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Stair Calculator

Top floor is final tread; no code or structural certification.

Top floor is final tread; no code or structural certification.

Your workbenchInputs are not stored

Result

Enter your values and run the tool to see your result.

What this tool does

Works out the number of risers, the actual riser height, and the horizontal run from total rise, a target riser height, and tread depth. It assumes the upper floor serves as the final tread.

How to use it

  1. Enter the total rise in centimetres, finished floor to finished floor.
  2. Enter the target riser height.
  3. Enter the tread depth.
  4. Run it for the riser count, actual riser height, and run.

Worked example

A 280 cm rise with an 18 cm target riser and 28 cm treads gives 16 risers, an actual riser of 17.5 cm, and a 420 cm run.

Calculation method

Riser countceil(rise/target)
Actual riserrise/ceil(rise/target)
Horizontal run(ceil(rise/target)-1)*tread

Frequently asked questions

The actual riser is lower than my target.
Because the rise must divide into a whole number of risers, the count is rounded up. 280 ÷ 18 is 15.6, so 16 risers, and 280 ÷ 16 is 17.5 cm. All risers must be equal for safety.
Why is the run based on one fewer tread?
The upper floor acts as the last tread, so treads number one less than risers: 16 risers means 15 treads, and 15 × 28 = 420 cm.

What this tool does not cover

Geometry only — no code or structural check. Confirm riser and tread limits, handrails, headroom, and landing requirements against your local building code.

References