Stair Stringer Calculator
Enter total rise and stair width to get IRC-compliant riser height, number of treads, stringer length, and the exact 2×12 and tread lumber you need.
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Top Pick2×12×16 Stringer Lumber — Home Depotfrom $24.98* Affiliate links — we may earn a commission at no cost to you.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
How many stairs do I need for a 42-inch rise?
A 42-inch total rise divided by the ideal 7.5-inch riser height gives 5.6, rounded to 6 risers. With 6 risers, each riser is exactly 7 inches — within IRC's 7.75-inch maximum. You will have 5 treads.
What is the 7-11 rule for stairs?
The 7-11 rule states that a comfortable stair has a riser height of about 7 inches and a tread depth of about 11 inches. Together, riser + tread should sum to approximately 17–18 inches for a comfortable stride.