The stair stringer calculator determines the dimensions and materials needed to build the support beams (stringers) that hold up a staircase. **Stringer Length** = √(total rise² + total run²), where total run = treads × tread depth **Number of Steps** = risers − 1 (the number of notches cut into the stringer) **Board Feet (for 2×12 stringer)** = 2 × stringer length (in feet) Stringers are typically made from 2×12 lumber, which is nominal 2" thick and 12" wide. Each stringer runs diagonally from the base to the top of the staircase. The board feet calculation assumes standard 2×12 stringer material; if using a different size, adjust accordingly. Most residential stairs use 2-3 stringers for adequate support.