Rebar Sizing Guide for Ontario — 10M, 15M, 20M Explained
If you’re new to Ontario concrete work, the rebar sizing system can trip you up — especially if you came up reading American spec sheets. Canada uses the metric “M” designation (10M, 15M, 20M, 25M) while the US uses #3, #4, #5, #6. Same bars, different labels.
This guide tells you exactly which size for which job, when to spec epoxy-coated, how spacing works, and what we stock at our three GTA yards.
The Canadian rebar size chart
| Designation | Nominal Diameter | Cross-Section Area | Mass per metre | US equivalent |
|---|---|---|---|---|
| 10M | 11.3 mm | 100 mm² | 0.785 kg/m | #3 (3/8”) |
| 15M | 16.0 mm | 200 mm² | 1.570 kg/m | #5 (5/8”) |
| 20M | 19.5 mm | 300 mm² | 2.355 kg/m | #6 (3/4”) |
| 25M | 25.2 mm | 500 mm² | 3.925 kg/m | #8 (1”) |
| 30M | 29.9 mm | 700 mm² | 5.495 kg/m | #10 (1-1/4”) |
10M and 15M cover ~90% of GTA residential and light commercial work. 20M and up are structural / engineered.
Which size for which job
10M rebar
- Slab-on-grade temperature steel (4” residential basement slabs, garage floors).
- Crack-control mesh substitute in non-structural slabs.
- Light footings under non-load-bearing walls.
- Sidewalk and walkway reinforcement.
15M rebar — the workhorse
- Foundation walls for residential basements (8” walls, typically 15M @ 12” or 16” o.c. vertical, with horizontals at 24” o.c.).
- Strip footings under foundation walls.
- Structural slabs in residential and light commercial.
- Retaining walls under 4 ft.
- Slab-on-grade where heavier loads are expected (commercial floors, garage aprons, warehouse pads).
If a residential drawing doesn’t specify a size, it’s almost always 15M.
20M rebar
- Commercial foundations.
- Engineered beams and columns in residential.
- Heavy retaining walls.
- Parking garage slabs.
- Engineered floor slabs with point loads.
25M and 30M
- Major structural — bridge work, large commercial buildings, transfer slabs.
- Rarely used in residential. If a residential plan calls for 25M, your engineer has a reason — don’t substitute down.
Black rebar vs epoxy-coated
Black rebar (standard): carbon steel, no coating. Use anywhere it’s encapsulated in concrete and not exposed to road salt, chlorides, or weather.
Epoxy-coated (green) rebar: thin epoxy coating on standard rebar. Pay extra for:
- Bridge decks, road slabs, parking garages.
- Anywhere salt-laden water can reach (driveways near road, exterior slabs in salting routes).
- Coastal exposure (not a GTA issue but if you work outside Ontario, factor it in).
- Code-mandated jobs (Ministry of Transportation Ontario specs).
Handling rule: Once the epoxy coating is chipped, it’s compromised. Cap the ends and tie carefully — don’t drag epoxy bars across rough surfaces.
We stock both black rebar and epoxy-coated rebar in all common sizes.
Spacing — the rule of thumb
For Ontario residential foundations:
- Foundation walls: 15M @ 12” or 16” o.c. vertical, 15M @ 24” o.c. horizontal.
- Strip footings: 2 × 15M continuous, top and bottom (4 total) for a typical 16” footing.
- Slabs-on-grade with reinforcement: 10M or 15M @ 12” o.c. each way.
- Wire mesh substitute: 6 × 6 W2.9 × W2.9 (152 × 152 MW19 × MW19).
These are typical guidelines — always defer to your engineer’s drawings for anything load-bearing.
Dowels — the often-forgotten part
A dowel is a smooth rebar that’s epoxied into existing concrete to tie new concrete to it. Common in slab extensions, additions, and curb-to-slab connections.
Standard dowel sizes in the GTA:
- 10mm dowels — slab-on-grade extensions, light tie-ins.
- 15mm dowels — foundation wall tie-ins, heavier slabs.
- 20mm dowels — structural connections.
We stock both smooth dowels and the epoxy-coated rebar dowels for chloride-exposed work.
Accessories you need with rebar
Don’t show up to a pour with just rebar — you also need:
- Rebar chairs (plastic or steel) — hold bars at the right height in the concrete. Match the height to the slab depth.
- Tie wire — 16-gauge black annealed steel (or PVC-coated for visible work). We stock both at all three yards.
- Pliers / tying tools — the manual hook or the spinner. Manual is fine for small jobs; if you’re tying a whole foundation, get the spinner.
- Bar cutters / benders — if you’re not buying pre-cut bars, you’ll need these on site. We rent and sell.
All available in Hand Tools and Steel Rebar categories.
Buying tips for GTA contractors
- Buy from a yard that stocks the lengths you need. Standard rebar lengths are 6 m / 20 ft. If you need 12 ft or 8 ft pre-cut, ask first. We do custom cuts.
- Order an extra 5–10%. Rebar gets bent, miscounted, and stolen. Don’t run short.
- Get a delivery quote. Rebar is heavy and ties up a flatbed. Yard pickup is fastest for small orders; for foundation jobs, we’ll deliver same or next day.
- Mind the storage. Wet rebar rusts fast. Light surface rust is fine (it actually bonds better to concrete), but heavy flaking rust gets rejected by inspectors.
Need rebar today?
We carry 10M, 15M, 20M black rebar and epoxy-coated rebar in all common lengths at our Brampton, Mississauga, and Pickering yards. Volume pricing for contractors and same-day delivery across the GTA.
Browse all rebar → Request a quote → Call: 647-926-2597