The following is a rule-of-thumb formula for interior stairs, as specified in the Architectural Graphic Standards.
- Riser + Tread = 17.5 inches (445mm): 7.5 inches (191mm) for the riser height; 10 inches (254mm) for the tread depth.
- Riser * Tread = 75 inches (1905mm).
- 2(Riser) + Tread is greater than or equal to 24 inches (610mm) (minimum threshold) or less than or equal to 25 inches (635mm) (maximum threshold).