10M rebar is the smallest standard Canadian reinforcing bar: 11.3 mm in nominal diameter (0.445 in), 100 mm² in area, weighing 0.785 kg per metre. The "M" means metric and the 10 is a rounded label, not the diameter. In imperial terms it falls between US #3 (3/8 in) and #4 (1/2 in) bar, and it is not the same as either.
Here is everything that is specific to 10M in one place: the dimensions, what it weighs by length, how tight it can be bent, typical lap lengths, and where it shows up in real buildings and in the Ontario Building Code.
10M rebar dimensions and weight
The nominal values come from CSA G30.18, the Canadian standard for carbon-steel reinforcing bar, as published in the Reinforcing Steel Institute of Canada (RSIC) Manual of Standard Practice.
| Property | 10M value |
|---|---|
| Nominal diameter | 11.3 mm (0.445 in) |
| Cross-sectional area | 100 mm² (0.155 in²) |
| Nominal perimeter | 35.5 mm |
| Mass | 0.785 kg/m (0.528 lb/ft) |
| Weight of a 6 m bar | about 4.7 kg |
| Weight of a 12 m bar | about 9.4 kg |
| Metres per tonne | about 1,274 m |
| Standard mill length (RSIC) | 12 m |
Note that 10M is the one size the RSIC manual lists with a 12 m standard mill length. 15M and larger are 18 m. That matters when laying out long runs, since every bar beyond 12 m needs a lap.
The nominal diameter is a weight-equivalent figure: the diameter of a plain round bar that weighs the same per metre. Measure a 10M bar across its ribs and you will read more than 11.3 mm. For the full size range, see our Canadian rebar size chart.
Is 10M rebar 3/8 or 1/2 inch?
This is the most common question about 10M, and the honest answer is that it is neither.
| Bar | Diameter | Area |
|---|---|---|
| US #3 (3/8 in) | 9.5 mm | 71 mm² |
| Canadian 10M | 11.3 mm (about 7/16 in) | 100 mm² |
| US #4 (1/2 in) | 12.7 mm | 129 mm² |
So a 10M bar carries about 41% more steel than a #3 and about 22% less than a #4. If an American detail calls for #4 at a given spacing, 10M at the same spacing gives you less steel. If it calls for #3, 10M gives you more.
Two more traps:
- US "#10" is not 10M. US soft-metric bar labels use millimetres too, and a #10 soft-metric bar is the US #3 (9.5 mm). A US #13 is the #4. Our Canadian vs US rebar sizes post explains the naming.
- Fiberglass "10M" is not steel 10M. Some GFRP bars sold as 10 mm have a nominal area of 71 mm², the same as US #3.
Any substitution between systems changes the steel in the member, so it needs the designer's approval.
Bending 10M: bend diameters and hooks
10M is easy to bend in a shop, which is why it is the go-to size for stirrups, ties and small bent shapes. Bends still have minimum diameters under CSA A23.1, and the RSIC manual turns those into standard hook dimensions:
| Item | 400W or 500W | 400R or 500R |
|---|---|---|
| Minimum finished bend diameter, standard hooks | 60 mm | 70 mm |
| 90° hook detailing allowance | 180 mm | 180 mm |
| 180° hook detailing allowance | 130 mm | 140 mm |
| Stirrup and tie bend diameter | 45 mm | 45 mm |
| 135° stirrup and tie hook allowance | 100 mm | 100 mm |
The hook allowances are what a detailer adds to the bar length on the bar list, so they show up directly in the bar's weight. Our post on rebar hook lengths gives the full tables for every size.
Hand bending 10M on site is possible, but getting a consistent bend diameter and hook length is another matter. Pre-bent corner bars, dowels and stirrups arrive tagged and correct.
Lap and development length for 10M
Lap lengths for 10M depend on concrete strength, where the bar sits and whether it is coated, so the number on your drawings governs. For a sense of scale:
- CSA A23.3 simplified method, uncoated Grade 400 bar in 30 MPa concrete: a Class B tension lap of about 390 mm for bottom bars and about 510 mm for top bars. Development length is about 300 mm, the code minimum for a straight bar in tension.
- Ontario Building Code, flat ICF walls: where Part 9 allows prescriptive ICF construction, it requires 10M laps of at least 450 mm.
Our lap splice length chart shows all the assumptions behind these figures. Epoxy-coated 10M needs longer laps again.
Where 10M rebar is used
In general practice, 10M is the size for light reinforcement and for bent pieces:
- Slabs on grade that are reinforced, especially thinner residential slabs where a bigger bar would eat into the cover. See 10M vs 15M for a concrete slab.
- Stirrups and column ties in beams and columns of all sizes.
- Light walls, including ICF walls and the horizontal bars in many foundation walls.
- Temperature and shrinkage steel in walls and slabs where the design calls for a light grid.
- Small dowels, corner bars and trim bars around openings.
Where the Ontario Building Code names 10M
The 2024 OBC is mostly silent on bar size, because reinforced concrete is designed under Part 4 by an engineer. The exceptions are prescriptive Part 9 details, and 10M appears in several:
- Flat ICF foundation walls (Article 9.15.4.5.): horizontal reinforcement of one 10M bar within 300 mm of the top of the wall plus 10M bars at no more than 600 mm on centre. Vertical bars come from tables by wall thickness and backfill height, and many of those entries are 10M.
- ICF dowels to the footing (Article 9.15.4.4.): one way to treat an ICF foundation wall as laterally supported at the bottom is dowels of 10M at no more than 600 mm on centre (or 15M at 1.2 m).
- Above-grade flat ICF walls (Article 9.20.17.2.): the same horizontal 10M pattern, with vertical 10M bars at no more than 400 mm on centre.
- Openings in ICF walls (Articles 9.20.17.3. and 9.20.17.4.): 10M bars around openings in non-loadbearing walls, and 10M stirrups in lintels over openings wider than 1,200 mm in loadbearing walls.
- Slabs over cold rooms (Section 9.40.): small reinforced slabs over basement cold rooms use 10M bars at no more than 200 mm each way, anchored to the walls with bent 10M dowels.
Each of these comes with conditions on wall height, thickness, openings and backfill. Treat this list as a map of where to look, not as a design, and read the full article or get your designer to confirm.
10M vs 15M in one line
One 15M bar has twice the area and twice the weight of one 10M bar. So 10M at 200 mm carries the same steel as 15M at 400 mm. The engineer picks between them based on member thickness, cover, crack control and how the bars will be placed. The full comparison is in our 15M rebar guide.
Ordering 10M rebar
Most 10M on a job is not straight stock. It is stirrups, ties, dowels, corner bars and cut-to-length mats, which is where a bar list pays off: every piece is cut, bent, tagged by mark and bundled, so the crew is not sorting or bending on site.
We detail, cut and bend 10M to 55M bar and deliver across the GTA and Ontario. Send your drawings for a free take-off and quote, or see our rebar products.
Frequently asked questions
What size is 10M rebar?
10M rebar has a nominal diameter of 11.3 mm (0.445 in), a cross-sectional area of 100 mm² and a mass of 0.785 kg per metre under CSA G30.18. It is the smallest standard Canadian bar size.
Is 10M rebar 3/8 or 1/2 inch?
Neither. At 11.3 mm, 10M sits between US #3 (3/8 in, 9.5 mm) and #4 (1/2 in, 12.7 mm). It has about 41% more steel than #3 and about 22% less than #4, so swapping either for 10M needs the designer's approval.
Is 10M rebar 10 mm in diameter?
No. The 10 is a rounded label. The nominal diameter of 10M bar is 11.3 mm, which is the diameter of a plain round bar with the same weight per metre.
How much does a 12 m length of 10M rebar weigh?
About 9.4 kg. 10M weighs 0.785 kg per metre, so 12 × 0.785 = 9.42 kg. A 6 m piece is about 4.7 kg.
What is 10M rebar used for?
Slabs on grade, ICF and light concrete walls, stirrups and ties, and general residential work. The Ontario Building Code also names 10M for several prescriptive ICF wall details and for small reinforced slabs over cold rooms.
