A standard 90° hook on Canadian Grade 400W or 500W rebar adds 180 mm for 10M, 250 mm for 15M, 300 mm for 20M and 400 mm for 25M to the bar's detailed length. A 180° hook adds 130, 170, 200 and 280 mm for the same sizes. These are the hook allowances in the Reinforcing Steel Institute of Canada (RSIC) Manual of Standard Practice, built on the hook definitions and minimum bend diameters in CSA A23.1.
This post is the length reference: the full table, the formulas behind it, worked examples and how hook length feeds into a cut length. For what each hook type is used for, see our guide to standard rebar hooks.
Rebar hook length table, 10M to 55M
D is the finished bend diameter. A or G is the hook allowance used in detailing. J is the overall height of a 180° hook, out-to-out.
Grade 400W or 500W (weldable)
| Bar size | D | 90° hook A or G | 180° hook A or G | 180° hook J |
|---|---|---|---|---|
| 10M | 60 mm | 180 mm | 130 mm | 80 mm |
| 15M | 90 mm | 250 mm | 170 mm | 120 mm |
| 20M | 100 mm | 300 mm | 200 mm | 140 mm |
| 25M | 150 mm | 400 mm | 280 mm | 200 mm |
| 30M | 200 mm | 490 mm | 350 mm | 260 mm |
| 35M | 250 mm | 590 mm | 430 mm | 320 mm |
| 45M | 400 mm | 770 mm | 630 mm | 490 mm |
| 55M | 550 mm | 1,010 mm | 850 mm | 660 mm |
Grade 400R or 500R
| Bar size | D | 90° hook A or G | 180° hook A or G | 180° hook J |
|---|---|---|---|---|
| 10M | 70 mm | 180 mm | 140 mm | 90 mm |
| 15M | 100 mm | 260 mm | 180 mm | 130 mm |
| 20M | 120 mm | 310 mm | 220 mm | 160 mm |
| 25M | 150 mm | 400 mm | 280 mm | 200 mm |
| 30M | 250 mm | 510 mm | 400 mm | 310 mm |
| 35M | 300 mm | 610 mm | 480 mm | 370 mm |
| 45M | 450 mm | 790 mm | 680 mm | 540 mm |
| 55M | 600 mm | 1,030 mm | 900 mm | 710 mm |
The values are from the 2020 RSIC manual. Some older charts in circulation show slightly smaller 180° allowances for 45M and 55M, so if two charts disagree, go with the edition your detailer and engineer are working to.
Stirrups and ties are different: they use smaller bends and their own hook table (100 mm for 10M and 140 mm for 15M). Those are covered in stirrup sizes and hook lengths.
The rebar hook length formula
CSA A23.1 defines the standard hooks by their bend and their straight extension:
- 90° hook: a 90° bend plus an extension of at least 12 bar diameters at the free end.
- 180° hook: a semicircular bend plus an extension of at least 4 bar diameters, but not less than 60 mm.
RSIC turns those definitions into detailing allowances:
- 90° hook: A = 12 db + D/2 + db
- 180° hook: G = (4 db, minimum 60 mm) + π × (D + db) ÷ 2 − D/2 − db
where db is the bar diameter and D is the finished bend diameter from the rebar bending chart. The results are rounded to the nearest 10 mm.
What the pieces mean:
- For the 90° hook, A is the out-to-out length of the hooked leg: the 12 db extension, plus the bend radius, plus one bar thickness.
- For the 180° hook, the π term is the length of the bar around the semicircle, measured along its centreline. The two subtractions remove the part of the bend already counted in the straight dimension the hook is attached to.
Worked examples
15M, Grade 400W, 90° hook. db = 16.0 mm, D = 90 mm. A = 12 × 16.0 + 90 ÷ 2 + 16.0 = 192 + 45 + 16 = 253 mm, which rounds to 250 mm.
20M, Grade 400W, 180° hook. db = 19.5 mm, D = 100 mm. 4 db = 78 mm, which is more than 60 mm, so use 78. G = 78 + π × (100 + 19.5) ÷ 2 − 50 − 19.5 = 78 + 187.7 − 69.5 = 196 mm, which rounds to 200 mm.
10M, Grade 400W, 180° hook. db = 11.3 mm, D = 60 mm. 4 db = 45 mm, which is less than 60 mm, so the 60 mm minimum governs. G = 60 + π × 71.3 ÷ 2 − 30 − 11.3 = 60 + 112.0 − 41.3 = 131 mm, about 130 mm.
The last example shows why small bars have relatively long 180° hooks: the 60 mm minimum extension governs, not 4 bar diameters.
Bend radius for 10M, 15M and 20M rebar
The bend radius people ask about is half the bend diameter, measured to the inside of the bar:
| Bar size | 400W or 500W inside radius | 400R or 500R inside radius | Stirrup and tie inside radius |
|---|---|---|---|
| 10M | 30 mm | 35 mm | about 23 mm (45 mm pin) |
| 15M | 45 mm | 50 mm | about 33 mm (65 mm pin) |
| 20M | 50 mm | 60 mm | same as main bars |
The radius to the centre of the bar is larger by half a bar diameter: about 36 mm for a 10M W-grade main bar, 53 mm for 15M and 60 mm for 20M. That centreline radius is what goes into length calculations.
Hooks in a cut length
On a bar list, every dimension is out-to-out of the bar, except the A and G hook dimensions on 135° and 180° hooks. To estimate the total length of a hooked bar, add the hook allowances to the straight detailing dimensions.
Example: a 15M Grade 400W footing bar, 2,400 mm long out-to-out, with a 90° hook at each end.
- Straight dimension: 2,400 mm
- Two 90° hooks: 2 × 250 = 500 mm
- Estimated length: 2,900 mm, or about 4.6 kg of 15M at 1.570 kg/m
Detailers round bar lengths to the nearest 20 mm under RSIC practice, and the simple sum slightly overstates the true developed length because it counts the corner twice. For estimating tonnage, that small overstatement is normal. Our rebar estimating guide shows how hook allowances add up across a job.
Coated bar hooks are longer
Epoxy-coated and galvanized bar need larger bends, which lengthens the hooks. From the RSIC tables:
| Bar size | Epoxy 90° hook | Epoxy 180° hook | Galvanized 90° hook | Galvanized 180° hook |
|---|---|---|---|---|
| 10M | 190 mm | 150 mm | 160 mm | 130 mm |
| 15M | 270 mm | 200 mm | 240 mm | 170 mm |
| 20M | 330 mm | 260 mm | 320 mm | 220 mm |
| 25M | 430 mm | 330 mm | 430 mm | 330 mm |
Epoxy-coated bars also need longer development and lap lengths; see epoxy-coated rebar lap length.
Hook length is not anchorage length
A hook's length is a fabrication dimension. Whether the hook anchors the bar is a design question. CSA A23.3 gives a development length for a bar ending in a standard hook, measured from the critical section to the outside of the hook, and that length depends on bar size, concrete strength, cover and confinement. Our guide to rebar development length explains it.
When a hook does not fit, the answer belongs to the engineer, not the bending table. Options include a restricted J dimension on 180° hooks, a 180° hook in place of a 90° hook, headed bars or a change of bar size. Bend diameters cannot be reduced by more than 10% from the standard values without the engineer's permission.
Get hooked bars made to the table
Hooks are where small errors show up on site: a 90° hook 50 mm long hits the formwork, and a short one may not anchor. Shop bending to the RSIC allowances keeps every hook on a mark identical.
Procut details, cuts and bends 10M to 55M rebar in our Erin shop, with each bundle tagged by mark. Send us your drawings or bar list for a free take-off and quote, or see our rebar products.
Frequently asked questions
How long is a 90 degree hook on 15M rebar?
On Grade 400W or 500W bar, the RSIC detailing allowance for a 90° hook on 15M is 250 mm, measured out-to-out. On 400R or 500R bar it is 260 mm because the bend diameter is larger.
What is the rebar hook length formula?
For a 90° hook, RSIC uses A = 12 bar diameters + half the bend diameter + one bar diameter. For a 180° hook, G = 4 bar diameters (at least 60 mm) + π × (D + db) ÷ 2 − D ÷ 2 − db, where D is the finished bend diameter and db the bar diameter.
What is the bend radius for 10M, 15M and 20M rebar?
For 400W or 500W bar, the minimum inside bend radius is 30 mm for 10M, 45 mm for 15M and 50 mm for 20M (half of the 60, 90 and 100 mm bend diameters). R grades are 35, 50 and 60 mm.
Is hook length the same as development length?
No. Hook length is the fabrication allowance for the hooked end. Development length of a hooked bar is the embedment the engineer needs to anchor it, measured from the critical section, and it comes from CSA A23.3.
