Stair calculator

Work out the stairs for your deck

Enter the height of your deck: we work out how many steps you need, how tall they are, how long the stringers are and what to buy, then check it all against the Québec Construction Code.

  • No construction know-how needed: every measurement is explained with a drawing.
  • Feet and inches or centimetres, your choice.
  • A scale drawing of your stairs that updates as you type.
01

Measure the height to climb

From the top of the deck boards down to the ground, at the spot where the stairs will land.

Total height

ft
in
cm

Measuring it right

  • Measure from the top of the deck boards, not from underneath them.
  • Measure where the bottom step will land, not right beside the deck: yards are rarely flat.
  • Sloped yard? Lay a long straight board on the deck, level it, and measure from the board down to the ground at that spot.
  • A pad or pavers planned at the bottom? Measure to their finished surface.
How to measure the total height: a straight board, levelled on the deck, reaches out to where the stairs will land, and you measure from the board down to the ground. Deck Level Straight board Total height Landing pad
02

Choose the boards for the steps

Each step is made of two boards. Their width sets how deep the steps are; their thickness sets the cut at the foot of the stringers.

03

Stair width

Most deck stairs are 3 to 5 feet wide. The code asks for at least 860 mm (34 in).

Width

ft
in
cm
Advanced options Optional. The defaults suit most decks.
Where the stairs start

How far each tread sticks out over the step below. The code limits it to 25 mm (1 in).

Code check

The Québec Construction Code limits for an outdoor stair serving a single home. Your municipality may ask for more.

    Cuts and materials

    Rough quantities for shopping or comparing quotes. Allow a little extra.

      The vocabulary

      The parts of a deck stair

      The words the calculator uses, shown on a drawing. Each number points to one part of the stairs.

      Side view of a deck stair with its parts numbered 1 to 10 1 2 3 4 5 6 7 8 9 10
      1. Total height (total rise) From the top of the deck boards down to the ground where the stairs land. It is the measurement everything starts from.
      2. Total run The ground the stairs take up, from the deck to the bottom step.
      3. Riser The height of one step. All of them must match, within 5 mm.
      4. Tread Where your foot goes, usually two boards side by side.
      5. Run The depth of one step: the horizontal distance from one nosing to the next.
      6. Nosing The front edge of a tread, sticking out a little over the step below.
      7. Stringer The board cut in a sawtooth pattern, usually a 2×12, that carries the treads. Wider stairs need more of them.
      8. Landing pad The solid, level surface at the foot of the stairs.
      9. Handrail The rail you hold on the way up. Required from 4 risers.
      10. Guard The barrier that stops a fall off the deck. Required once the drop is more than 600 mm (24 in).

      The rules

      Deck stair rules in Québec

      The calculator applies these Québec Construction Code limits for an outdoor stair that serves a single home, what the code calls a private stair.

      Part Requirement Good to know
      Step height (riser) 125 to 200 mm (5 to 7 7/8 in) All equal in a flight: at most 5 mm between two steps and 10 mm across the whole flight.
      Run 255 to 355 mm (10 to 14 in) Measured horizontally, from one nosing to the next.
      Tread depth The run to the run + 25 mm So the nosing sticks out by 25 mm (1 in) at most.
      Width 860 mm (34 in) minimum 36 to 48 in (91 to 122 cm) is more comfortable.
      Handrail More than 3 risers One side is enough for a house, 865 to 1,070 mm (34 to 42 in) high.
      Guard A drop of more than 600 mm (24 in) 900 mm (36 in) high, or 1,070 mm (42 in) when the deck is more than 1.8 m above the ground; openings under 100 mm (4 in).
      Height of one flight 3.7 m (about 12 ft) maximum Above that, a landing part-way is required.
      Stringers At least 90 mm (3 1/2 in) of wood below the notches A 2×12 leaves enough every time; a 2×10 only with low steps.

      Source: Québec Construction Code, Chapter I – Building (NBC 2020 as amended for Québec), section 9.8, private stairs. Your municipality may be stricter: check before you build. This calculator is for planning; it does not replace a drawing or a professional’s advice.

      Questions

      Deck stairs: your questions

      What South Shore homeowners ask us most before building stairs.

      For 36 in (91 cm), plan on 5 risers of about 7 3/16 in (18.3 cm). The deck itself is the top step, so there are 4 treads to build, and with two-board composite treads the stairs reach about 3 1/2 ft (1.06 m) into the yard.

      For a stair serving a single home, the Québec Construction Code allows 125 to 200 mm (5 to 7 7/8 in) per riser, with a run of 255 to 355 mm (10 to 14 in). Every step in a flight must match within 5 mm. Outdoors, steps of 6 to 7 1/2 in are the most comfortable.

      As soon as an outdoor stair has more than 3 risers. For a house, a handrail on one side is enough, 865 to 1,070 mm (34 to 42 in) high. The deck itself needs a guard once it is more than 600 mm (24 in) above the ground.

      It depends on the width and the boards. Composite makers usually ask for a stringer every 12 in (30 cm), and some lines every 9 in, so 4-foot stairs need 5. Pressure-treated 2 × 6 treads can span up to 16 in. The calculator does the count for you.

      Measure where the bottom step will land, not at the foot of the deck. Lay a long straight board on the deck, level it, and measure from the board down to the ground at that spot. If a pad or pavers are planned, measure to their finished surface.

      The classic comfort rule, known since the 17th century as Blondel’s formula: two riser heights plus one run should come to 60 to 65 cm, about 24 to 25 1/2 in, which is the length of a natural stride. A 7 in riser with a 10 1/2 in run gives 24 1/2 in: stairs that climb easily.

      It depends on your city. New stairs are usually part of the deck’s permit application, and some cities also ask for one to replace stairs. Check with your municipality before the work starts; for our clients, we prepare the application documents.

      Ready to build?

      Stairs that are solid, up to code and good-looking

      We build composite, PVC and pressure-treated stairs on the South Shore and across Montérégie, stringers, guards and landing pad included. Send us your result and we check the measurements on site.

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