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Calculate stair dimensions, riser and tread counts, stringer length, and material quantities from floor-to-floor height.
Measure the floor-to-floor height in inches. This is the vertical distance from the surface of the lower finished floor to the surface of the upper finished floor. For a standard 9-foot ceiling with typical floor construction, this is usually about 108 inches.
The calculator divides total rise by your target riser height (default 7 inches) and rounds to the nearest whole number. It then recalculates the exact riser height by dividing the total rise evenly among all risers, ensuring uniform steps.
The number of treads is always one less than the number of risers (the top “tread” is the upper floor itself). Total horizontal run equals treads times tread depth. This tells you how much floor space the staircase needs.
Using the Pythagorean theorem (diagonal = sqrt of rise² + run²), the calculator determines the length of each stringer. This is the length of 2x12 lumber you need to cut each stringer from.
The calculator checks your stairs against IRC residential code limits: max riser height (7.75″), min tread depth (10″), and comfortable angle (under 42°). Warnings alert you to any values that may not meet code requirements.
A well-designed stair follows the “rule of comfort”: riser height + tread depth should equal approximately 17-18 inches. With the default values of 7″ risers and 11″ treads, you get 18″ — right in the comfort zone. Adjusting one dimension affects the feel of the stairs significantly.
Total vertical distance from finished floor to finished floor (9 ft = 108 in)
Comfortable target: 7 in. IRC max: 7.75 in.
IRC minimum: 10 in. Comfortable: 11 in.
IRC minimum: 36 in. 3 stringers for 36 in, 4 for 48 in
Each 7.2" tall
11" deep each
154" horizontal
188.1" diagonal
Within comfortable range
For 36" width
12 ft boards for stringers