Stair Calculator

The short answer

The comfort rule is that twice the riser plus the tread should land between 24 and 26 inches. A 7-inch riser with an 11-inch tread gives 25. For a total rise of 108 inches, 16 risers at 6.75 inches or 15 risers at 7.2 inches both work. Dividing the total rise into equal risers, with the number of treads one fewer than the number of risers, is the core calculation.

What it depends on

Codes set maximum riser and minimum tread dimensions, and the limits vary by jurisdiction — a common maximum riser is around 7.75 inches with a minimum tread near 10 inches. Headroom, landings and handrails are separate requirements, and landings are typically required for runs over about 12 feet. The bottom and top risers are where mistakes concentrate, because the floor thickness has to be accounted for.

Where this stops being useful

This is a proportion calculation for planning. Stairs are structural and code-governed items, and requirements cover riser uniformity, headroom, guard and handrail geometry, lighting and landing dimensions. A structural engineer or building inspector can confirm what applies locally. General information and planning only, not engineering, structural or code advice.

Two measurements decide a staircase: the total rise and the available run. The rise is the floor-to-floor height, and it is fixed by the building. The run is the horizontal distance available, and it decides how comfortable the stairs are. Building codes set limits on the rise per step, the going per step, headroom and the width of the stair itself — a comfortable private stair is not the same as one that passes inspection, and the codes get stricter for anything serving more than one dwelling.

Stairs are the element most likely to be discovered as a problem late in a build, because they are often fitted after everything else. Working out the rise and the run early, while there is still flexibility in the floor plan, is far cheaper than moving a wall later.

Standard riser and going dimensions come from a small number of combinations, and using one of them saves both material and headroom problems. Once the total rise is divided by a standard riser you get a step count, which gives the going required — and if that does not fit the available run, the stair has to change shape, not just dimensions. Check headroom at the midpoint and above the landing, since that is where low beams usually are. Balustrade spacing is also code-controlled and is checked separately from the stair itself.

Stairs are governed by a simple idea: every step must be identical. You begin with the total rise, the vertical distance from one finished floor to the next, and divide it into a whole number of equal risers. That last word is the crux — a staircase with a slightly taller final step is a trip hazard, and building codes require risers to match closely, so the number of risers is chosen to make each one come out even. Comfort comes from the relationship between rise and going. A widely used rule is that twice the riser plus one tread should land near twenty-five inches: around seven-inch risers with ten-inch treads, or six-and-a-half with twelve. Steeper stairs feel abrupt and are hard to descend; shallower ones take up more floor space. The total run is the tread depth multiplied by the number of treads, which is one fewer than the number of risers because the top step lands on the floor above. Headroom and layout constrain the design more than the arithmetic. The run of the stair has to fit the available space, and the nosing, that small overhang at the front of each tread, adds to the effective depth without changing the structural cut. The stringer, the sloped beam that carries the steps, is the hypotenuse of the rise and run, and cutting its notches accurately is what makes the finished stair level and even. This calculator gives the number of risers, their height, treads, total run, stringer length and the resulting angle. It assumes a straight flight with no landing and a standard code-like geometry, and it does not cover railings or non-standard local requirements. Check your local building code before cutting, since permitted riser and tread dimensions are regulated.

This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.