How to choose rebar stock sizes in Ontario
This step-by-step guide helps Ontario contractors and concrete crews read metric bar designations, match sizes (10M–55M) to slab, footing and structural uses, confirm which sizes are normally stocked in the GTA, and complete a concise takeoff-to-order checklist so orders arrive on time.
1. Read the labels: understand Canadian M designations
Canada uses the metric “M” designation for reinforcing bars: 10M, 15M, 20M and so on. Each M number corresponds to a standard nominal diameter in millimetres. The government designation table lists common bar numbers and diameters, for example 10M is 11.3 mm, 15M is 16.0 mm, and 20M is 19.5 mm. For an authoritative reference see the CBSA list of bar designation numbers and diameters.
If drawings mix Canadian and American notation, remember the physical bar is the same even if labels differ. Regional supplier guides also publish practical cross-references to help when U.S. # notation appears on engineer drawings.
Quick conversion chart: common sizes and uses
| Designation | Diameter (mm) | Typical on-site use |
|---|---|---|
| 10M | 11.3 | Slab-on-grade, temperature and shrinkage bars, light reinforcement |
| 15M | 16.0 | Foundation walls, shallow footings, many structural slabs |
| 20M | 19.5 | Heavier slabs, beams, moderate columns |
| 25M | 25.2 | Columns, larger beams, heavy footings |
| 30M | 29.9 | High-load structural elements |
| 35M | 35.7 | Very heavy structural sections |
| 45M | 43.7 | Large infrastructure applications |
| 55M | 56.4 | Specialized heavy reinforcement |
Source references: CBSA bar designation list and regional supplier sizing guides provide the authoritative mapping used on Canadian contracts and customs documents.
2. Match sizes to common uses on Ontario sites
Apply this practical rule of thumb when reading shop drawings or preparing a takeoff. These uses reflect typical GTA practice on residential and light commercial jobs and are a starting point when the specification is not explicit.
- 10M (11.3 mm): slab-on-grade mesh, temperature steel, small residential details.
- 15M (16.0 mm): foundations, footings, basement walls, many structural slabs.
- 20M (19.5 mm): primary reinforcement for heavier slabs, beams, and moderate columns.
- 25M and above: large columns, deep footings, municipal or infrastructure elements with high design loads.
When in doubt, consult the project engineer before changing bar sizes. Regional buying guides for Mississauga and Brampton provide useful context on how contractors typically use these sizes on GTA sites.
3. Which sizes the GTA usually stocks and when you need a special order
Many Ontario rebar suppliers keep common sizes in stock so crews can avoid mill lead times. For standard residential and light-commercial projects, 10M, 15M and 20M are frequently held as inventory. Larger diameters and specialty items such as epoxy-coated bars or uncommon lengths are more likely to require a mill order.
Two factors commonly force a special order: the specified grade and the coating. For example, specifying epoxy-coated Grade 500W for corrosive exposure can add lead time. Supplier stock lists vary, so always confirm real-time availability before committing to a schedule. Regional buyer guides also list everyday stocked sizes and typical procurement expectations.
4. Takeoff to order: a step-by-step checklist
Follow these ordered steps to convert drawings into a confirmed purchase and avoid site delays.
- Prepare a grouped bar list: for each designation record drawn length, required finished length, piece count and total linear metres. Group identical items to simplify quoting.
- Specify grade and finish: list Grade 500W or 400W, and note epoxy-coated or GFRB if required.
- Attach marked drawings: include plan and section pages that show locations, splices and lap lengths so the supplier sees context.
- State fabrication scope: indicate if you want cut-and-bend, welded mats, cage assembly or on-site tying. Include bend schedules and tolerances.
- Request a stock check and quote: ask the supplier which items are immediate stock and which require mill orders, and supply desired delivery windows.
- Confirm delivery constraints: give the supplier site address, offload capability, and delivery hours so they can plan the truck size and timed delivery.
- Issue a purchase order: once terms and lead times are confirmed, issue a PO with project reference and required compliance documentation.
For local notes on cut delays and stocked sizes in Woodbridge, see the Dass Rebar supplier note on Reo Steel in Woodbridge: Cut Delays with Stocked Sizes.
5. What to provide your supplier: exact documents and details
Send this packet with your quote request to get an accurate and fast reply:
- Bar list with designation, length, quantity, grade and coating
- Marked drawings showing layout, splices and anchorage
- Bend schedules and fabrication tolerances
- Site access notes, delivery hours, and offload constraints
- Procurement requirements such as MTO paperwork for infrastructure jobs
Providing complete information up front reduces clarifying calls and speeds the supplier’s stock check and pricing.
6. Questions to ask and decision rules to confirm availability
Use these exact questions when you call or email a supplier. They help you decide whether to accept a stocked substitute or wait for special-order material.
- Which of these designations are available for immediate pick-up or delivery?
- Are the listed bars Grade 500W, 400W, or another grade, and do you stock epoxy-coated options?
- What are the estimated lead times for mill-ordered sizes or coated bars?
- Can you provide shop drawings and a fabrication schedule and what is the expected fabrication window?
- Do you hold MTO approval for provincially funded projects and can you provide the documentation?
Decision rule example: if the project critical path depends on an immediate foundation pour, prefer stocked 15M or 10M substitutes where the engineer permits. If the specification requires epoxy-coated Grade 500W, plan for a longer procurement window and secure written lead-time confirmation.
7. MTO and procurement considerations for infrastructure work
Infrastructure and provincially procured projects often require MTO-approved materials and documented traceability. Confirm the supplier’s MTO-approved status and request material certificates or mill test reports with the quote. Dass Rebar lists MTO-approved supplier status among its qualifications, but always request the specific certification the contract demands before placing a purchase order.
8. Delivery, on-site assembly and storage best practices
Plan delivery and short-term storage to prevent damage and schedule slips. Provide realistic delivery windows and access notes. Reserve a dry, level storage area that keeps bars off the ground, and protect bundled material from standing water. Arrange an offloading plan for heavy bundles, and confirm whether the supplier or your crew will perform final assembly or tying.
Dass Rebar operates a dedicated trucking fleet and offers project coordination, discuss coordinated delivery windows early when you place the order to match routing to your schedule.
9. When to specify epoxy-coated rebar or GFRB
Specify epoxy-coated rebar for elevated corrosion risk, for example exposed parking slabs, coastal structures or areas where de-icing salts are used. Glass Fibre Reinforcing Bars, or GFRB, are a non-metallic alternative where long-term corrosion resistance is a priority. Include coating or GFRB requirements in the initial quote packet so the supplier can confirm stock or lead times.
10. Common supplier objections and practical next steps
Common responses and how to react:
- No immediate stock of a specific size: ask for a stocked substitute that meets the engineer’s minimum diameter and reassess lap and splice details with the engineer.
- Mill lead time for coated or nonstandard lengths: consider phasing pours or changing bar lengths to match stocked cut lengths where design and code allow.
- Fabrication backlog: request staged fabrication or partial deliveries of critical items first.
Final checklist and next step
- Complete bar list with designations and millimetres confirmed
- Grade and coating specified (Grade 500W or 400W, epoxy or GFRB)
- Marked drawings and bend schedules attached
- Stock check requested and lead times received in writing
- Delivery window and site access confirmed
- MTO or other procurement paperwork requested if required
When you are ready to confirm a site-specific stock check or request a quote, Dass Rebar accepts project quote requests through their site, and they list local capability and stock of common sizes and mesh. For supplier-specific notes on avoiding cut delays, see the Dass Rebar article on Reo Steel in Woodbridge: Cut Delays with Stocked Sizes.
Frequently asked questions
What do 10M, 15M and 20M mean and how do they convert to millimetres?
They are Canadian metric bar designations. For example, 10M is 11.3 mm, 15M is 16.0 mm and 20M is 19.5 mm. Consult the government designation table for the authoritative list of sizes from 10M to 55M.
Which rebar sizes are usually stocked by suppliers in the GTA and Ontario?
For most residential and light-commercial work in the GTA, 10M, 15M and 20M are the most commonly stocked sizes. Larger diameters and coated or specialty bars are more likely to require a mill order. Always request a live stock check before scheduling installation.
When should I specify epoxy-coated rebar or GFRB instead of standard rebar?
Specify epoxy-coated rebar where corrosion risk is elevated, such as exposed parking slabs, coastal structures, or areas frequently treated with de-icing salts. GFRB is appropriate when a non-metallic reinforcement solution is required. Include this requirement in the initial quote so the supplier can confirm availability and lead time.
How do I prepare a rebar takeoff so a supplier can give an accurate quote?
Prepare a grouped bar list showing designation, length, quantity and grade, attach the marked drawings and bend schedules, and include site access and delivery constraints. The more complete the packet, the faster the supplier can confirm stock, fabrication capacity and price.
How do Canadian M sizes map to US number sizes if my engineer used American notation?
Canada uses M numbers and the U.S. typically uses the # system. The same physical bar can appear under different labels. Use a regional cross-reference chart from a supplier guide to verify exact equivalence before ordering if drawings mix notations.
Key takeaway: read the M designation, match sizes to the job, request a live stock check, and send a complete takeoff packet to the supplier to avoid delays.
Authoritative references and regional guides: CBSA rebar designation list, and a regional sizing guide for Ontario: Rebar sizes Ontario. For a supplier stock check and project quote, visit Dass Rebar contact or the Dass Rebar homepage at the official website.