Deck stair rise and run: how many steps do you need?

Checked 14 November 2026 · General guidance for Australia and the United States

To work out how many steps your deck needs, measure from the top of the decking down to where the stairs will land, divide by a comfortable riser height and round up. In Australia every riser must be 115 to 190 mm and every going 240 to 355 mm (NCC 2022 Housing Provisions Part 11.2). In the US a riser can be at most 7¾ in. and a tread at least 10 in. deep (IRC R311.7.5). A 900 mm deck works out to six risers of 150 mm.

What are the rise and run rules for deck stairs?

The riser is the height of each step. The going (Australia) or tread depth (US) is how far you move forward on each step, measured nosing to nosing.

These are the model codes. States, councils and local building departments can amend them, and the 2024 IRC moves the stair rules to R318.7 without changing these limits. Your builder, certifier or building department has the final say.

How many steps do I need for my deck?

Steps are counted as risers. Divide the total rise by a comfortable riser height, round up to a whole number, then divide the rise by that number to get the actual riser. The deck itself is the top step, so a flight always has one fewer tread than it has risers.

Measure the rise where the bottom step will land, not at the deck post. On a sloping yard the ground there can be lower than it is under the deck, which adds a riser. Land the flight on a firm, level pad.

Worked example: a 900 mm deck in Australia

1. A comfortable riser is around 175 mm. 900 ÷ 175 = 5.1, so round up to 6 risers.
2. 900 ÷ 6 = 150 mm per riser, inside the 115 to 190 mm range.
3. 2R = 300 mm, so for 2R + G to sit between 550 and 700 the going must be 250 to 400 mm. The 355 mm limit caps it at 250 to 355 mm.
4. A going around 300 mm is easy to walk. Five treads at 300 mm make a flight about 1.5 m long.

Five risers of 180 mm would also pass, with goings of 240 to 340 mm. That flight is shorter but steeper. At 900 mm the stairs rise less than 1 m, so the NCC doesn’t require a handrail or balustrade on them, though a handrail still helps.

Worked example: a 36 in. deck in the US

1. Aim for risers of about 7¼ in. 36 ÷ 7.25 = 4.97, so 5 risers.
2. 36 ÷ 5 = 7.2 in. per riser, under the 7¾ in. maximum.
3. Four treads of at least 10 in. At 10½ to 11 in. each the run is 42 to 44 in.
4. Five risers is four or more, so the flight needs a handrail. The deck is also more than 30 in. above grade, so it needs a guard around it.

When do deck stairs need a handrail?

Gap and height rules for the railing itself are in the deck railing height guide.

How far apart should stair stringers be?

The code sets rise and going. How far apart the stringers go is set by the tread material, and composite treads need far more support than timber.

Check your decking maker’s current installation guide before you cut. Deckulator draws cut stringers from the deepest joist size it uses, 240 × 45 in Australia and 2×12 in the US, and adds enough of them to keep each tread within its maker’s span.

What else should I check?

• Slip resistance (Australia). The NCC asks for treads rated P3 (R10) where they stay dry and P4 (R11) where they can get wet, which outdoor stairs can.
• Doors onto stairs (Australia). Where a door opens onto stairs that rise more than three risers or 570 mm, you need a landing at least 750 mm long first.
• Treads from whole boards. Stair treads look best made from a whole number of deck boards, so the going often ends up set by your board width plus gaps, less a small nosing.

This guide explains common rules in plain words. It isn’t engineering advice: span tables, footings and barriers depend on your timber grade, soil, wind and local rules. Have a builder, certifier or building department check your design before you build.