Quick answer: To build deck stairs, divide the deck height by about 7 inches for the number of risers, multiply the run (usually 11 in) by the treads for total run, and take the diagonal — √(rise² + run²) — for the stringer length. Land the stairs on a concrete pad.
This deck stair calculator turns your deck height into the number of steps, riser and run, stringer length and count, stair angle, and the landing pad size — sized for outdoor deck stairs to grade.
Deck stairs run from the deck surface down to grade, so your "total rise" is measured to the finished ground — not floor to floor. Because they live outdoors and often carry more foot traffic, deck stairs use a slightly gentler ratio than interior stairs.
Deck stringers attach to the deck rim joist with a ledger board, angle brackets, or a notched connection, and they must land on a solid, level surface. A poured concrete pad or a compacted paver landing prevents the bottom step from sinking and shifting over time. Size the pad at least as wide as the stairs and about 36 inches deep for a safe standing area.
Measure the total height from the top of the deck to the finished ground, divide by about 7 inches for the number of risers, then divide the total height by that count for the exact riser height. Multiply the tread depth (usually 11 inches for two 2x6 boards) by the number of treads for total run.
Deck stairs are usually more relaxed than interior stairs: about a 6.5 to 7 inch riser and an 11 inch run. The IRC allows a maximum 7.75 inch riser and requires a minimum 10 inch tread.
Space stringers no more than 18 inches apart for 2x wood treads and 12 to 16 inches for composite. A 48 inch wide stair typically needs 4 stringers.
Yes. Deck stairs should land on a solid, level surface — a concrete pad or paver landing at least as wide as the stairs and about 36 inches deep so there is a safe standing area at the bottom.
The IRC requires a graspable handrail on at least one side of any stair with four or more risers. Guards are also required where the walking surface is more than 30 inches above grade.
The stairs extend out by the total run. For example, a 40 inch high deck needs about 6 steps, and at an 11 inch run that projects roughly 55 inches (about 4.5 feet) out from the deck.