How to use this stair calculator
- Unit, choose inches or centimetres so every result matches your measurements.
- Total rise, measure the vertical height from the lower finished floor to the upper finished floor and enter it.
- Target riser height, set the step height you want to aim for (about 7 in or 18 cm is typical).
- Tread depth, enter how deep each step is from front to back (about 11 in or 28 cm is typical).
- Read the number of steps, riser height, total run and stringer length, they update instantly as you type.
Nothing is submitted or stored: the numbers never leave your device, so you can sketch out a staircase privately.
How stairs are calculated
The starting point is the number of steps. You take the total floor-to-floor rise and divide it by your target riser height, then round to the nearest whole number, because every step has to be the same height:steps = total rise / target riser (rounded). A 108 in rise with a 7 in target gives about 15 steps.
Once the step count is fixed, the actual riser height is the total rise shared equally across those steps:riser = total rise / steps. With 108 in over 15 steps each riser is 7.2 in. Thetotal run is the horizontal distance the stairs cover. Because the top step lands on the upper floor, you multiply the tread depth by one less than the step count: total run = (steps - 1) x tread depth.
Finally the stringer length, the long diagonal board that supports the steps, is found with Pythagoras. It is the diagonal of a right triangle whose two sides are the total rise and the total run:stringer = sqrt(rise^2 + run^2). A typical comfortable staircase aims for a riser of around 7 in and a tread of around 11 in, which together feel natural to climb.
Check your local building code
These figures are a fast planning estimate, not a construction drawing. Maximum riser height, minimum tread depth, headroom, handrails and landings are all governed by your local building code, and the limits differ from one region to another. Always confirm every dimension against the rules that apply where you live, and have load-bearing work checked by a qualified builder before you cut a single board.
Frequently asked questions
How many steps do I need?
Divide your total floor-to-floor rise by your target riser height and round to the nearest whole number. A 108 in rise with a 7 in target gives about 15 steps.
What is a comfortable riser and tread?
A riser of about 7 in (18 cm) and a tread of about 11 in (28 cm) suits most people. Your local building code sets the legal limits, so always check it.
How is stringer length worked out?
The stringer is the diagonal of the staircase, so it equals the square root of the total rise squared plus the total run squared.
What does total run mean?
Total run is the horizontal distance the staircase covers. It is the number of steps minus one, multiplied by the tread depth.
Does this follow building codes?
No, it gives quick estimates only. Allowed riser heights, tread depths and headroom vary by region, so confirm everything against your local building code before building.