Stair Calculator

The most important rule in stair building is Uniformity. The human brain quickly "maps" the height of the first few steps; if any subsequent step varies by more than 3/8 of an inch, the user is likely to trip. This is why our calculator divides the total rise into an even number of steps, often resulting in a fractional riser height like 7-1/8 inches. Never round these numbers to the nearest whole inch; use a "story pole" or a precise tape measure to layout your stringer cuts. Additionally, pay attention to the "7-11 Rule": for maximum comfort, a riser should be no more than 7.75 inches and a tread should be at least 10-11 inches deep. This balance ensures the stairs aren't too steep or too shallow for an average adult stride.

Construction of the Stair Stringer is another critical area. For most residential stairs, "Cut Stringers" are made from 2x12 pressure-treated lumber (for decks) or high-grade pine (for indoors). You should never use 2x10s for stringers, as the "throat" of the board (the uncut part) will be too thin to support the weight of a person safely. For stairs wider than 36 inches, you must use at least three stringers—one on each side and one in the middle—to prevent the treads from bowing or "bouncing" when walked upon. Our calculator provides the "Stringer Angle" to help you set your miter saw or layout your framing square. Finally, don't forget about Headroom and Handrails. Most codes require at least 6'8" of vertical clearance above every step and a handrail between 34 and 38 inches high. Our tool helps you with the steps, but these secondary safety features are what make your staircase professional and legal.