20M rebar is a Canadian metric bar with a nominal diameter of 19.5 mm (0.768 in), an area of 300 mm² and a mass of 2.355 kg per metre. 25M rebar is 25.2 mm (0.992 in), 500 mm² and 3.925 kg per metre. Both are made to CSA G30.18. 20M is the nearest Canadian bar to a US 3/4 inch (#6) bar, and 25M is the nearest to a 1 inch (#8) bar. They are the step up from 15M for footings, columns, beams, walls and structural slabs that carry more load.
This guide covers what is specific to the two sizes: dimensions, weights by length, inch equivalents, bend and hook sizes, laps, and where you meet them on drawings, including the Ontario Building Code.
20M and 25M rebar dimensions and weight
Nominal values come from CSA G30.18 and are published in the Reinforcing Steel Institute of Canada (RSIC) Manual of Standard Practice.
| Property | 20M | 25M |
|---|---|---|
| Nominal diameter | 19.5 mm (0.768 in) | 25.2 mm (0.992 in) |
| Cross-sectional area | 300 mm² (0.47 in²) | 500 mm² (0.78 in²) |
| Nominal perimeter | 61.3 mm | 79.2 mm |
| Mass per metre | 2.355 kg/m (1.582 lb/ft) | 3.925 kg/m (2.637 lb/ft) |
| Weight of a 6 m bar | about 14.1 kg | about 23.6 kg |
| Weight of a 12 m bar | about 28.3 kg | about 47.1 kg |
| Weight of an 18 m bar | about 42.4 kg | about 70.7 kg |
| Metres per tonne | about 425 m | about 255 m |
Two quick ratios help when you compare options on a drawing:
- One 20M has 1.5 times the steel of a 15M. So 20M at 300 mm and 15M at 200 mm put the same area of steel in a metre of wall or slab.
- One 25M has 2.5 times the steel of a 15M and about 1.67 times a 20M.
"Nominal diameter" is the diameter of a plain round bar that weighs the same per metre. The ribs stick out past it, so a tape or caliper over the ribs reads more. Our post on rebar diameter with ribs explains why.
How big is 20M and 25M rebar in inches?
| Bar | Diameter | Area | Nearest match |
|---|---|---|---|
| US #6 (3/4 in) | 19.1 mm | 284 mm² | |
| Canadian 20M | 19.5 mm (about 3/4 in) | 300 mm² | US #6, 20M has about 6% more steel |
| US #7 (7/8 in) | 22.2 mm | 387 mm² | no Canadian equivalent |
| Canadian 25M | 25.2 mm (about 1 in) | 500 mm² | US #8, 25M has about 2% less steel |
| US #8 (1 in) | 25.4 mm | 510 mm² |
The pairs are close, but they are not the same product. Canadian bars follow CSA G30.18 with Canadian grade markings (400W, 500W and so on), and US bars follow ASTM standards. The US #7 sits between 20M and 25M with no Canadian neighbour, which catches people converting American details. Any substitution is an engineering decision. Also watch for US soft-metric labels: a "#19" bar is the US #6 and a "#25" bar is the US #8, not Canadian sizes.
Bending 20M and 25M: bend diameters and hooks
At 20M and up, bending by hand on site is no longer realistic, and a portable bender struggles with consistent results. Almost every bent 20M and 25M bar is shop fabricated. CSA A23.1 sets the minimum bend diameters, and the RSIC manual gives the hook allowances detailers use:
| Item | 20M, 400W or 500W | 20M, 400R or 500R | 25M, all grades |
|---|---|---|---|
| Minimum finished bend diameter, standard hooks | 100 mm | 120 mm | 150 mm |
| 90° hook allowance | 300 mm | 310 mm | 400 mm |
| 180° hook allowance | 200 mm | 220 mm | 280 mm |
| 180° hook overall height (J) | 140 mm | 160 mm | 200 mm |
Those hook allowances are a large share of a short bar. A 25M dowel with a 90° hook carries 400 mm of bar in the hook alone, so hooks must be on the bar list and in the tonnage from the start. Epoxy-coated and galvanized bars need bigger bends and longer hooks again. The full tables are in our guide to rebar hooks and bend radius.
Lap and development length for 20M and 25M
Laps grow with bar size, and they jump sharply between 20M and 25M because the bar size factor in CSA A23.3 changes from 0.8 (20M and smaller) to 1.0 (25M and larger). For uncoated Grade 400 bar in 30 MPa concrete, using the A23.3 simplified method:
| Length | 20M | 25M |
|---|---|---|
| Tension development length, bottom bars | about 520 mm | about 830 mm |
| Class B tension lap, bottom bars | about 670 mm | about 1,080 mm |
| Class B tension lap, top bars | about 870 mm | about 1,400 mm |
| Compression lap splice (RSIC table) | 590 mm | 730 mm |
The tension numbers assume minimum cover, spacing and ties; the drawings govern, and your engineer may have used the more detailed method. The assumptions are spelled out in our lap splice length chart. The practical point is that a 25M lap can run more than a metre, which matters for congestion at splices and for how bars are cut from stock lengths.
Where 20M and 25M rebar is used
In general practice, 20M and 25M show up wherever a member needs more steel than 15M can sensibly provide at a buildable spacing:
- Columns and piers. 20M and 25M are common vertical bars in concrete columns. Under CSA A23.3, column ties must be at least 30% of the largest vertical bar's diameter, so 10M ties work for both, and tie spacing is limited to 16 times the smallest vertical bar's diameter (about 310 mm for 20M and 400 mm for 25M), as well as by the other limits in the standard. See rebar in concrete columns.
- Beams and grade beams. Bottom bars in beams and transfer members, often 20M or 25M with 10M or 15M stirrups.
- Heavier footings. Pad footings under columns, combined footings and raft slabs.
- Engineered walls. Retaining walls, shear walls and tall foundation walls with heavy backfill.
- Suspended and structural slabs. Bottom bars in thicker spans, and top bars over supports.
Bigger bars also mean fewer bars to place. One 25M carries the same area as five 10M, so engineers often choose larger bars where congestion or placing labour is an issue, within limits on spacing and crack control.
Where the Ontario Building Code names 20M and 25M
Most 20M and 25M work is engineered under Part 4. One prescriptive Part 9 table in the 2024 OBC uses both: Table 9.15.4.2.-B, reinforced concrete block foundation walls laterally supported at the top. In the taller and more heavily backfilled cases, it calls for continuous vertical bars of 20M (for example in 240 mm block walls) and, in a few 190 mm wall cases with high backfill, 25M as an alternative to paired 15M bars or closer-spaced 20M. Each entry depends on wall thickness, wall height and the height of finished ground, so read the table with your designer rather than picking a bar from it. Our post on rebar in concrete block walls covers grouting and placement.
Handling and ordering 20M and 25M
- Weight per piece adds up. An 18 m 25M bar is over 70 kg. Long bars of this size are handled with equipment or by several people, which is another reason to order them cut to length.
- Stock lengths and laps. Long laps on 25M make it worth having the detailer plan splice locations and cut lengths, so offcuts are not wasted.
- Bends are shop work. L-bars, hooked dowels, U-bars and column offsets in these sizes should arrive bent and tagged.
- Check the grade. 400W is the everyday grade, but 500W and other grades are specified on some jobs. The grade is rolled onto the bar and shown on the bar list.
For a typical foundation or column package, 20M and 25M usually arrive alongside 10M ties and 15M bars, all cut, bent and tagged by mark so the crew can place them straight off the truck.
Getting 20M and 25M bar on your job
We detail, cut and bend rebar from 10M to 55M in our shop and deliver across the GTA and Ontario, including fabricated dowels, stirrups and custom bent shapes. Send us your structural drawings for a free take-off and quote, or see our rebar products for the full size chart.
Frequently asked questions
What size is 20M rebar?
20M rebar has a nominal diameter of 19.5 mm (0.768 in), a cross-sectional area of 300 mm² and a mass of 2.355 kg per metre under CSA G30.18. It is the Canadian bar closest to US #6 (3/4 inch).
What size is 25M rebar?
25M rebar has a nominal diameter of 25.2 mm (0.992 in), an area of 500 mm² and a mass of 3.925 kg per metre. It is the Canadian bar closest to US #8 (1 inch).
How thick is 20M rebar in mm?
The nominal diameter is 19.5 mm. A caliper across the ribs reads more than that, because the nominal diameter is the diameter of a plain round bar with the same mass per metre.
Is 20M rebar 3/4 inch?
Close. US #6 is 3/4 inch (19.1 mm, 284 mm²). 20M is 19.5 mm with 300 mm², about 6% more steel. They are made to different standards, so a substitution goes through the engineer.
How much does a 20M or 25M bar weigh?
An 18 m stock length of 20M weighs about 42.4 kg, and of 25M about 70.7 kg. Per metre that is 2.355 kg and 3.925 kg.
