Design / Structural
Stair Stringer Calculator (Rise / Run / Code Check)
Plan a stair stringer: rise, run, number of treads, headroom, and IRC code check.
Calculator
What makes this different
Most calculators stop at 'rise + run'. This one checks the IRC 7-11 rule (rise + run between 17 and 18 in is comfortable), flags treads that would be too narrow, and shows whether your headroom meets the 6 ft 8 in minimum.
Who it's for & when to use it
Building a deck stair, a basement stair, or a shop loft ladder.
How to use
- Enter the dimensions of your material or the parameters of your project.
- Adjust the optional knobs (waste factor, kerf, planer allowance) to match your shop practice.
- Click Calculate and read the output. Use the per-item breakdown for ordering, the totals for budgeting.
- Compare the result to your lumber yard's quote — the effective $/BF column is the apples-to-apples number.
Formula: Treads = ceil(total_rise / 7.5). Riser height = total_rise / treads. 7-11 rule: 2 × riser + tread_run ≈ 25 in.
Notes & tips from the shop
- IRC requires a maximum 7.75 in riser and a minimum 10 in tread (11 in for spiral). Local amendments can be stricter.
- Each riser must be within 3/8 in of the others across the run. Measure twice.
- Open risers are allowed on most residential stairs but prohibited on stairs serving more than one dwelling.
Frequently asked questions
What if my total rise doesn't divide evenly?
Adjust the bottom or top riser by 1/4–1/2 in to keep all the others equal. Never vary the middle risers.
Can I use 2×12 for stringers?
Yes, but a notched 2×12 has less wood at the narrowest point. Use 2×12 for short spans, deeper for longer.
Do I need a landing?
IRC requires a landing if the stair has more than 12 ft of rise. Door landings have additional width rules.
Limitations
Single straight run. Winder stairs, L-stairs, and curved stairs need additional geometry.
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