Size deck stair stringers from grade to deck: riser, tread, board recommendation, stringer count and landing triggers.
Deck stairs add three concerns to the basic geometry. First, the stringer board must keep at least 3.5 inches of sound wood behind each notch — the throat. If a 2x10 can't hold that, the calculator calls for a 2x12. Second, stringer spacing of 16 or 24 inches on-center determines how many stringers the width needs. Third, a single flight may not exceed the code's maximum rise between landings; cross that and the tool flags that a landing is required.