Deck Stair Calculator
Deck height in, steps out. It keeps every riser under the 7¾ inch code limit and tells you the run, the stringer length and how many stringers to buy.
The arithmetic
Divide the total rise by 7.75 inches and round up. That gives the number of risers, because the residential code and the American Wood Council DCA 6 deck guide cap a riser at 7¾ inches. Divide the rise by that count for the actual riser height, so every step is the same. You get one fewer tread than risers, because the deck itself is the top step.
Treads must be at least 10 inches deep. Two 5/4x6 boards with a gap give about 11¼ inches, which is comfortable.
The rules this follows
From DCA 6: stringers at least 2x12; stairs at least 36 inches wide; at least three cut stringers, spaced no more than 18 inches on center; a handrail 34 to 38 inches high on any stair with four or more risers; and an intermediate landing if the total rise is over 12 feet. Stair footings sit at least 12 inches below undisturbed ground or below the frost line, whichever is deeper. Your local building department can amend any of this, so check before you build.
What this leaves out
Measure the rise from the deck surface to where the bottom step will land, not to the ground under the deck, since the ground often slopes. For footings under the deck itself, use the deck footing calculator. For the whole job, the deck cost calculator, or see our deck building page.
Common questions
How many steps do I need for my deck?
Divide the height from the deck surface to the landing by 7.75 inches and round up. A 36 inch rise needs 5 risers of 7.2 inches.
What is the maximum riser height for deck stairs?
7¾ inches, under the residential code and the AWC DCA 6 guide. Minimum tread depth is 10 inches.
How many stringers do deck stairs need?
At least three cut stringers for a 36 inch stair, spaced no more than 18 inches on center, per DCA 6.
What size lumber for deck stair stringers?
2x12 minimum, per DCA 6.
When do deck stairs need a handrail?
With four or more risers, at 34 to 38 inches high, per DCA 6.
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