Free Online Staircase Dimension Calculator
Calculate stair rise, run, treads, and angle.
Building codes vary by location and by stair type. Use this calculator for planning, then confirm the final dimensions with your local code official or a qualified builder.
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About the Staircase Dimension Calculator
A comfortable staircase is a careful balance between rise and run. Rise is the vertical distance from one tread to the next; run is the horizontal depth of each tread. Get the ratio wrong and the stairs feel steep, shallow, or tiring even when they meet a building code. This calculator takes the total floor-to-floor rise and your preferred riser and tread dimensions, then works out the number of risers and treads, the total run, the stringer length, and the stair angle.
How the numbers fit together
The total rise is divided by the desired riser to choose a whole number of steps. Because the result is rounded, the actual riser will differ slightly from the preferred value; the calculator shows the exact height. The number of treads is one fewer than the number of risers, because the upper floor acts as the final tread. Total run is the tread count multiplied by the tread depth. The stringer length is the diagonal of the total rise and total run, which is the minimum length of board needed before allowances for cuts and landings.
The 2R + T comfort rule
A long-standing rule of thumb says that twice the riser plus the tread depth should fall between about 60 and 65 centimeters, or 24 and 25.5 inches. The rule captures the relationship between climbing height and foot space: steeper stairs need shallower treads, and generous treads allow a slightly higher riser. It is a guide rather than a code requirement, but it explains why 18 cm risers with 28 cm treads feel natural while 22 cm risers with 22 cm treads feel like a ladder.
Code, safety, and the things not calculated
Residential codes commonly limit riser height to around 19–20 cm (7.5–7.75 inches) and require a minimum tread depth of about 25 cm (10 inches), but the exact values depend on jurisdiction and occupancy. This calculator does not check handrail height, landing requirements, headroom, nosing projection, or the width of the stair. It also does not account for the thickness of finished flooring, which changes the total rise. Confirm those details before cutting stringers, and remember that a comfortable stair is not automatically a compliant one.
Frequently asked questions
Why is the actual riser different from the desired riser?
The total rise must be divided into equal steps, and the number of steps has to be a whole number. The calculator picks the closest whole number and divides the total rise by it. That keeps every riser identical, which is more important than matching the preferred value exactly.
How is the stringer length calculated?
It is the hypotenuse of a right triangle with the total rise as one leg and the total run as the other. Add extra length for the top and bottom cuts, and check the lumber size needed to span the distance safely.
Does this calculator check building codes?
No. It reports practical dimensions and the comfort rule, but code limits vary. Treat the output as a planning aid and verify riser height, tread depth, width, handrails, landings, and headroom with your local authority before building.