Deck Stair Calculator
Calculate deck stair rise, run, stringer length, footing requirements, and handrail length. Free calculator with printable diagram for exterior deck stairs.
Additional Requirements
How It Works
Enter your deck height from ground level, desired run per step, stair width, and number of stringers. The calculator uses the IRC maximum rise of 7-3/4" to determine the optimal number of steps.
Stringer spacing is the stair width divided evenly among the stringers. For example, 36" wide stairs with 3 stringers gives 18" on center.
Concrete footings at the base of each stringer prevent settling. The calculator assumes a standard 12"×12"×12" footing per stringer.
Handrail length is measured along the slope (hypotenuse) of the staircase, not the horizontal run. This is the actual length of rail material you need to purchase.
Frequently Asked Questions
How many stringers do I need for deck stairs?
Most building codes require stringers every 16 inches on center. For a standard 36-inch-wide staircase, 3 stringers is the norm — one on each side and one in the center. Wider stairs (48"+) may need 4 or more.
Do deck stairs need footings?
Yes. Deck stairs need a solid landing pad or individual footings at the base to prevent settling. A common approach is a 12"×12"×12" concrete footing at each stringer location, poured below the frost line in cold climates.
What is the maximum rise for exterior deck stairs?
The IRC limits the maximum riser height to 7-3/4 inches (196 mm) and requires a minimum tread depth of 10 inches. These limits apply to both interior and exterior residential stairs.
Do I need a handrail on deck stairs?
If your deck stairs have 4 or more risers (3 or more steps), the IRC requires a graspable handrail on at least one side, between 34 and 38 inches high measured vertically from the stair nosing.