How do I calculate the number of stairs?

Divide the total height from floor to floor by a comfortable riser height, around 180 to 190 mm, and round to a whole number of steps. Then divide the total height by that number for the exact riser. The calculator does this and checks the result is comfortable.

What is a comfortable riser and tread?

A common guide is twice the riser plus the tread, the going, should be about 600 to 640 mm. Risers around 180 mm and treads around 280 mm feel comfortable. The building code sets limits, so check the current rules for your project.

What is the total run of a staircase?

The total run is the horizontal distance the stairs cover. It is the number of treads times the tread depth. Knowing it helps you check the stairs fit the space available before you build.

Stair Calculator

Plan a staircase from the height it needs to climb. Enter the total rise, floor to floor, and your preferred tread depth, and the calculator works out a sensible number of steps, the exact riser height, and the total run. It also checks the rise and going against a comfort guide.

Total rise (mm)

Tread depth / going (mm)

Target riser (mm)

0 steps

number of risers

Riser height0 mm

Total run0 mm

Comfort (2R+G)0 mm

2R+G between about 600 and 640 mm is comfortable. Check the building code for your project.

How it works

The number of risers is the total rise divided by your target riser height, rounded to a whole number. The exact riser is then the total rise divided by that count. The treads are one fewer than the risers, and the total run is the treads times the tread depth.

Worked example

A 2,700 mm rise with a 190 mm target gives 14 risers, each about 193 mm. With 13 treads at 280 mm, the total run is 3,640 mm, and 2R+G is about 666 mm, a touch steep, so you might add a step.

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