Deck Stair and Stringer Calculator
Enter the height from your deck to the ground to get the number of steps, riser height, tread run, stringer length and how many stringers, all checked against the Ontario Building Code.
Risers
5 × 7-3/16"
Treads
4 × 10-1/2"
Total run
3' 6"
Stringers
4 × 2x12
See this deck in 3D
Opens our free 3D designer at deck height 3', with stairs. Try boards, colours, railings and stairs, then send it to us for a quote.
Stair layout
Deck stairs: 3' rise, 4 ft wide, pressure-treated 5/4x6 treads
Steps
- Risers7-3/16" each (183 mm); Ontario allows 125–200 mm
- 5
- TreadsThe top step is the deck itself
- 4
- Run per step267 mm; Ontario allows 255–355 mm
- 10-1/2"
- Tread depthTwo boards, nosing under 1 in
- 11-1/4"
- Total runFrom the deck edge to the last riser
- 3' 6"
Materials
- 2x12 stringers, 8 ft16 in on centre; 5-5/16" of wood left below the cuts (90 mm minimum)
- 4
- 12 ft pressure-treated 5/4x6 boardsCut into 8 tread pieces
- 3
Railings
- Handrail865–1070 mm (34–42 in) above the nosings
- Required
- Guards on open sides900 mm (36 in) from the nosing line, openings under 4 in
- Required
Based on the Ontario Building Code rules for private stairs serving one house (rise 125–200 mm, run 255–355 mm, risers within 5 mm of each other). Measure the rise after the landing pad is in, and confirm with your building department before you cut stringers.
Ontario stair rules this calculator follows
These are the Ontario Building Code limits for private stairs serving one house (OBC 2024, adopting National Building Code 2020 Section 9.8). Many online stair calculators use US rules, which differ on guard heights and the maximum run.
- Rise per step: 125–200 mm (4 7/8 to 7 7/8 in). The calculator aims for about 7 1/2 in, which is comfortable to climb.
- Run per step: 255–355 mm (10–14 in). The calculator uses 10 1/2 in, with two 5.5 in boards per tread.
- Width: at least 860 mm (about 34 in) for exterior stairs.
- Handrail above 3 risers, 865–1070 mm high. Guards where the stairs are more than 600 mm above the ground.
- One flight can rise at most 3.7 m before it needs a landing.
- Stringers keep at least 90 mm of solid wood below the notches, which is why it uses 2x12s.
Common questions
How many steps do I need for a 36 in high deck?
5 risers of 7-3/16" each, with 4 treads (the deck itself is the top step). At a 10-1/2" run per step the stairs reach out 3' 6" from the deck.
What is the maximum riser height for deck stairs in Ontario?
200 mm (7 7/8 in) for private stairs serving one house, and at least 125 mm (4 7/8 in). Every riser in a flight must match its neighbours within 5 mm and the whole flight within 10 mm, so measure the total rise after the landing pad is in.
How deep do stair treads need to be?
The run, measured nosing to nosing, must be 255–355 mm (10–14 in) for private stairs. The tread can be up to 25 mm (1 in) deeper than the run, which is the nosing. Two 5.5 in deck boards make an 11 1/4 in tread over a 10 1/2 in run.
How many stringers do deck stairs need?
It depends on the treads. 5/4 pressure-treated boards should be supported every 16 in, 2x6 treads every 24 in, and most composite treads every 12 in (some lines need 9 in). A 4 ft wide stair with 5/4 treads needs 4 stringers; with composite, 5.
When do deck stairs need a handrail in Ontario?
When there are more than 3 risers. The handrail sits 865–1070 mm (34–42 in) above the line of the nosings. Separately, guards are needed on any open side where the stairs are more than 600 mm above the ground.