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

This calculator works out how many steps a staircase needs and whether it will feel comfortable to walk, using the total height it has to climb and the tread depth you plan to use. You enter the total rise from floor to floor, your preferred tread depth or going, and a target riser height, typically around 180 to 190 mm. It returns the number of steps required, the exact riser height once the total rise is divided evenly across those steps, the total run, meaning the horizontal distance the staircase will cover, and a comfort check using the 2R+G rule, where twice the riser plus the going should sit between about 600 and 640 mm. This shows at a glance whether your planned dimensions feel too steep, too shallow, or about right, before you cut timber or order a stringer. Adjust the target riser or tread depth and watch the results update, to find a combination that fits the available floor to floor height and passes the comfort check. It is a handy first step when planning a new staircase, altering an existing one, or checking whether a supplier's design stacks up. Because building codes set limits on riser height, going and headroom that vary by building type, always confirm your final dimensions against the current code, and get your design checked by a qualified professional before construction begins.

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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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