Stair stringer calculator
- Total run: –
- Stringer length: –, buy a –
- – stringers, stair angle –
Measure total rise from the finished landing to the top of the finished deck or floor. Measure it plumb, not along a slope. This calculator assumes the deck itself is the top step, so there's one fewer tread than risers.
What I'd have on hand
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How the math works
Total rise is divided by your max riser height and rounded up to get the number of risers. Then the rise is split evenly across them. Treads are risers minus one, and the stringer length is the diagonal of total rise and total run.
When you lay it out with a framing square and stair gauges, remember to drop the bottom of the stringer by the thickness of one tread. Otherwise your first step comes out taller than the rest.
Common questions
What is the max riser height for deck stairs?
The IRC allows a maximum of 7¾″ per riser and a minimum tread depth of 10″. Risers in one flight can't vary by more than ⅜″. Some local codes are stricter.
How long of a board do I need for stair stringers?
Take the stringer length and add about a foot for the top and bottom cuts, then round up to the next even lumber length. Use 2x12s so there's enough wood left behind the cuts.
How many stringers do I need?
Space them no more than 16″ apart for wood treads. Most composite treads require 12″ spacing, so a 4 ft wide stair usually takes four or five stringers.