What Is the Stringer Calculator?
Calculate stringer dimensions with our free stringer calculator. Stringers are the structural backbone of any staircase - the diagonal boards that support the treads and risers. This tool computes stringer length, throat depth, notch dimensions, and the critical drop cut at the bottom.
How to Use This Calculator
- Enter total rise and tread depth (run per step).
- Set the stringer board width (typically 2×12 lumber).
- Review the calculated stringer length, throat depth, and notch dimensions.
- Verify the throat depth meets the minimum for structural integrity.
Why Accurate Stringer Calculations Matter
The throat depth - the narrowest point of the stringer after notching - determines structural capacity. Most building codes require a minimum throat depth of 3½ inches for residential stairs. Stringers that are too thin at the throat can crack under load.
Building Code References
Related Tools
Frequently Asked Questions
How many stringers do I need?+
Most stairs up to 36 inches wide need three stringers: two outer stringers and one center stringer. Stairs wider than 36 inches may need additional center stringers spaced no more than 18 inches apart.
What size lumber for stair stringers?+
2×12 pressure-treated or structural-grade lumber is standard. The 11¼-inch width provides adequate throat depth after cutting the notches for 7½-inch risers and 10-inch treads.