Deck Stair Calculator

Worked example

With these inputs:

• Total deck height (finished surface to ground): 42 in
• Preferred rise per step: 7" — most comfortable (recommended)
• Tread depth (run per step): 10-1/2" — two 5/4×6 boards with a gap
• Stair width: 42 in
• Cost estimate: DIY — materials only

Every rise must be within 3/8 inch of every other rise. Cut all stringers from one template, and remember to drop the bottom stringer by one tread thickness.

How it works

Enter your deck height and this calculator returns the number of steps, the exact rise per step, total horizontal run, stringer count, and an optional cost estimate — all inside IRC code limits.

Frequently asked questions

How many steps do I need for a 42-inch high deck?

Six steps at exactly 7 inches of rise each. That gives five treads and a total run of about 52 inches with 10-1/2 inch treads. The sixth 'step' is the deck surface itself.

What is the maximum rise for deck stairs?

The IRC allows a maximum riser height of 7-3/4 inches for residential stairs and a minimum tread depth of 10 inches. All risers on one flight must be within 3/8 inch of each other.

How many stringers do I need for deck stairs?

Three stringers minimum for stairs up to 36 inches wide with 2x treads, four for 42-48 inch stairs, and five for 60-inch stairs. Composite treads need 12-inch spacing, which means more stringers.

Do I need a landing at the bottom of deck stairs?

Yes — the IRC requires a landing at least as wide as the stairs and at least 36 inches deep in the direction of travel. A 4-inch concrete pad or paver landing satisfies this and keeps the stringers off the soil.

Are box steps cheaper than stringer stairs?

For two or three steps, box steps (stacked frames) usually cost less and build faster. Above about 30 inches of total height, cut or pre-made stringers are cheaper and stronger.