Stair Stringer Calculator
Calculate every dimension you need to cut and build a code-compliant staircase. Enter total rise (floor-to-floor height), desired tread depth, and stair width to get: number of risers (calculated to divide evenly into total rise), actual riser height, number of treads, total horizontal run, stringer length (with overage for cuts), number of 2×12 stringers required (one per 24 inches of width), tread board count, and estimated lumber cost. The IRC requires a maximum 7.75-inch riser height and minimum 10-inch tread depth — the calculator flags if your configuration exceeds the maximum riser. Standard residential stairs use a 7.5-inch riser and 10-inch tread, which is close to the ergonomically optimal 7-11 ratio (riser + tread ≈ 17–18 inches).
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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.
How many stringers does a staircase need?
A staircase needs one stringer per 24 inches of width, with a minimum of 3 (two on the sides and one in the center). A 36-inch-wide staircase needs 2–3 stringers; a 48-inch stair needs 3. Each stringer is cut from a 2×12 board — the stringer length calculator gives you the minimum board length to order.
What is the minimum stair width required by code?
The IRC requires a minimum 36 inches of clear width for interior stairs in residential construction. This is measured between the handrail and the opposite wall (or between handrails). Exterior stairs serving a deck or porch have the same minimum, though 42–48 inches feels more comfortable for exterior use.