Deck Calculator for Ontario Decks
Enter your deck size and height to get a full materials list built on Ontario Building Code span tables: boards, joists, beams, posts, footings, concrete and railing. Then open it in 3D.
Deck area
192 sq ft
Deck boards
29
Joists
13 × 2x10
Posts & footings
3
See this deck in 3D
Opens our free 3D designer at 16 × 12 ft, 3' high. Try boards, colours, railings and stairs, then send it to us for a quote.
Materials list
Deck materials estimate: 16 x 12 ft (192 sq ft), 3' high, attached to the house
Decking
- 16 ft pressure-treated 5/4x6 boards26 rows across 12 ft, plus 10% for cuts
- 29
- Deck screwsTwo per board at every joist
- 710
Framing
- 2x10 joists, 12 ft16 in on centre
- 13
- Ledger, 2x10 × 16 ftFastened to the house rim joist
- 1
- Rim joist, 2x10 × 16 ft
- 1
- Joist hangers
- 13
- 1x4 mid-span strappingRequired on joists longer than 2.1 m
- 16 ft
- Beams, built up 3-2x83 pieces of 2x at 16 ft
- 1 beam
Posts and footings
- 6x6 posts3 per beam, about 8' apart
- 3
- 10 in concrete tubes, 1.2 m (4 ft) deepTops 150 mm (6 in) above grade
- 3
- Footing under each tubeSized for the load each post carries
- 20 in footing form
- 30 kg bags of concrete
- 21
Railing, stairs and permit
- Guard (railing)36 in (914 mm) high, openings under 4 in
- 36 ft
- Stairs7-3/16" each, 4 stringers, handrail required
- 5 risers
- Building permit in TorontoDecks more than 60 cm (24 in) above the ground
- Required
Guards built to Ontario’s SB-7 details are wood. Glass and aluminum railing systems need an engineered product.
A planning estimate for a rectangular deck using Ontario Building Code span tables (S-P-F No.1/No.2, 1.9 kPa live load). It is not a permit drawing. Your municipality’s rules, your soil and any hot tub or roof change what’s needed, so confirm with your building department before you build.
How the numbers are worked out
Most deck calculators online use US span tables and US railing rules. This one uses the Ontario Building Code (OBC 2024, which adopts the National Building Code 2020), cross-checked against Ontario municipal deck guides.
- Joists are sized from the code span table for spruce-pine-fir No.1/No.2 at a 1.9 kPa live load, using the conservative “with strapping” column. When no joist can span the full depth, it adds a beam in the middle.
- Beams are built-up 3-ply lumber from the code beam table, sized for the joists they carry, with posts no farther apart than the table allows.
- Posts are 6x6 (the code minimum) on 10 in concrete piers 1.2 m deep. Each footing is sized for the load its post carries, which is why most decks need a bell-shaped footing form under the tube.
- Concrete is counted in 30 kg premixed bags at about 0.014 m³ (0.5 cu ft) each, the yield the manufacturer publishes. A 10 in tube 4 ft long takes about 4.5 bags before the footing.
- Guards are required above 600 mm, at 900 mm high, or 1070 mm when the deck is more than 1.8 m above the ground.
What it doesn’t cover
- L-shaped, multi-level or curved decks. Work out each rectangle separately, or open the design in 3D and send it to us.
- Hot tubs, roofs or anything else that adds load. Those need an engineered design.
- Ledger fastening, flashing and connectors, which follow your permit drawings.
Common questions
How many deck boards do I need for a 16 x 12 deck?
About 29 boards at 16 ft. A 12 ft deep deck takes 26 rows of 5.5 in boards with a 1/8 in gap, each row 16 ft long, plus 10% for cuts and offcuts. With composite boards the gap is a little wider, so the count can go up by a board or two.
What size joists do I need for a 12 ft deck in Ontario?
At 16 in spacing, 2x10 joists. Under the Ontario Building Code span table for spruce-pine-fir No.1/No.2, a 2x8 spans 3.36 m (about 11 ft) at 16 in, so a 12 ft span needs a 2x10, which reaches 3.96 m (about 13 ft). Joists longer than 2.1 m also need a row of strapping or bridging at mid-span.
How deep do deck footings need to be in Ontario?
At least 1.2 m (4 ft) below finished grade in the GTA, to get below the frost. The pier usually stands about 150 mm (6 in) above grade. Small, low freestanding decks (55 m² or less and 600 mm or less to the underside of the joists) can sit on deck blocks instead.
When does a deck need a railing in Ontario?
When the deck is more than 600 mm (23 5/8 in) above the ground. The guard must be at least 900 mm (about 36 in) high, or 1070 mm (42 in) once the deck is more than 1.8 m up, with openings small enough that a 100 mm (4 in) ball can’t pass.
Do I need a permit for my deck?
In Toronto, a deck more than 60 cm (24 in) above the ground needs a building permit; lower decks that aren’t part of a required exit don’t, but zoning still applies. Other GTA cities set their own triggers, and some require a permit for any deck attached to the house. Check our deck permit guide for your city.
Does the calculator work for composite decking?
Yes. Pick composite and it switches from face screws to hidden clips (about 180 per 100 sq ft at 16 in spacing) and uses the wider composite gap. Most composite boards need joists at 16 in or closer, and 12 in for diagonal layouts.