The formula
How it works
Plan a staircase from the total height it must climb. Enter the floor-to-floor rise, a target riser height and your tread depth, and the calculator works out the number of steps, the exact riser height, the total run and the stringer length.
FAQ
What makes a comfortable step?
A common rule is that twice the riser plus the tread should be about 24–25 inches (63–64 cm). Risers around 7 inches with treads around 11 inches feel natural. The calculator divides the rise evenly so every step is identical, which is both safer and required by most building codes.
What is the stringer length?
It is the straight-line length of the diagonal board that supports the steps, found from the total rise and run with the Pythagorean theorem. Knowing it helps you buy timber of the right length and check the staircase will fit the space available.
Why does the calculator round the number of steps?
A staircase can only have a whole number of steps, so the target riser height is just a starting point. The calculator rounds to the nearest whole number and then recalculates the exact riser height so every step still comes out equal.
What if the riser height it gives seems too tall or too short?
Try a slightly different target riser height and see how the step count changes — moving the target by a fraction of an inch can shift the design to the next whole number of steps, which often lands much closer to what feels comfortable.
How much headroom do I need above the stairs?
Most codes call for at least about 80 inches (roughly 203 cm) of clear headroom measured vertically from the nose of each tread. This calculator does not check headroom, so measure the space above the stringer separately once you know the run.
Does the calculator account for the thickness of the flooring?
No — enter the true floor-to-floor rise, including any finished flooring or subfloor thickness at both the top and bottom, since even a small omission changes every riser height slightly.
What is stair pitch and why does it matter?
Pitch is the angle of the staircase from horizontal, and steeper stairs feel more like a ladder while shallower ones take up more floor space. Most comfortable interior stairs fall between about 30 and 35 degrees, which this calculator reports alongside the other measurements.
About the stair calculator
This calculator lays out a straight staircase from the total height it needs to climb. The key constraint is that every step must be the same height, so the rise has to divide into a whole number of equal risers. From your target riser height it finds the closest whole number of steps, then reports the exact riser height, the number of treads, the total horizontal run and the length of the stringer board.
How to use it
Enter the total rise — the floor-to-floor height — then a target riser height and your tread depth, choosing inches or centimetres. The calculator rounds to a whole number of steps and gives the exact riser height that results. For example, a 108-inch rise with a 7-inch target gives 15 risers of 7.2 inches each, 14 treads, a 140-inch run and a stringer of about 176.8 inches.
The formula
The number of risers is the rise divided by your target, rounded to a whole number, , and the actual riser height is then . There is always one fewer tread than riser, so the run is . The stringer follows the Pythagorean theorem, , and the pitch is the angle whose tangent is rise over run.
Where it is used
Builders, carpenters and DIYers use it to design stairs for decks, lofts, basements and porches before cutting any timber. Getting the riser height even and within code is essential for safety, and knowing the run in advance tells you whether the staircase will fit the floor space you have. It turns a single measurement — the height to climb — into a full cutting plan.