Under the Reinforcing Steel Institute of Canada (RSIC) Manual of Standard Practice, straight rebar is cut within ±25 mm, the overall length of a bent bar and most of its legs are held within ±25 mm, and stirrups and ties are bent within ±13 mm. Spirals are held to ±13 mm on diameter below 750 mm and ±25 mm above, and 90° bends may deviate by no more than 2°. If a detail needs better than that, the engineer has to say so on the drawings.
These are the standard fabricating tolerances for 10M to 55M bars, and they are what Canadian shops quote to unless a project specification asks for more.
Why rebar has fabrication tolerances
Rebar is cut by shears and bent cold on machines, at production speed, from bars that are themselves rolled to tolerances. RSIC's manual is direct about it: the nature of reinforcing steel, shop safety, the equipment used and the speed of production make tolerances necessary, and the standard values are ones that ordinary shop equipment can meet.
The concrete standard expects the same thing from the other side. CSA A23.1 requires bending to be accurate enough that the bars can still be placed within the placing and cover tolerances. In practice, the standard fabricating tolerances are set so that bars fit the forms and meet cover when they are detailed and placed properly.
The standard tolerance chart
RSIC Figure 6-1 shows the tolerances for typical bars. In table form:
| What is measured | Standard tolerance |
|---|---|
| Straight bar, sheared length | ±25 mm |
| Overall length of a bent bar | ±25 mm |
| Legs of hooked and L-shaped bars | ±25 mm |
| Height and overall length of truss (bent-up) bars | ±25 mm |
| U-shaped radius bends, width and height | ±25 mm |
| Stirrup legs | ±13 mm |
| Tie legs | ±13 mm |
| Spiral outside diameter, under 750 mm | ±13 mm |
| Spiral outside diameter, 750 mm and over | ±25 mm |
| Angle of 90° bends | ±2°, or a slope of 1 in 23 |
| Saw-cut ends for end bearing splices | Within 1.5° of square, within 3° of full bearing after assembly |
Radius-bent bars also have a tolerance on the curve itself, related to the bar length, which is shown on the same RSIC figure. Ask your fabricator how they check it if a curved wall or tank depends on it.
A ±13 mm tolerance on a stirrup leg sounds small, but it is a big share of a 40 mm cover. That is one reason stirrups and ties get the tighter number: they sit on the outside of the cage, right against the cover.
How the dimensions are measured
A tolerance only makes sense once you know what is being measured. RSIC rules:
- Out-to-out. All bar dimensions are measured to the outside of the bar, except A and G on standard 135° and 180° hooks, which are hook allowances rather than measured legs.
- Spirals are measured to the outside of the spiral.
- Lengths are detailed to the nearest 20 mm unless a dimension is flagged as critical.
- Critical dimensions. Where a bar must be bent more accurately than standard tolerance, the dimension is identified as critical on the bar list so the shop knows to hold it.
Bend type letters (A, B, C and so on) refer to the RSIC typical bar bends. If you need a refresher on which letter is which leg, see our guide to rebar bending shape codes.
Fabrication tolerance vs placement tolerance
These two are often confused, and both matter on site:
- Fabrication tolerance is how close each bar is to the bar list when it leaves the shop. It comes from RSIC standard practice.
- Placement tolerance is how close the bar is to its intended position once it is tied in the forms. It comes from CSA A23.1, with separate limits for cover, spacing, and the position of bends and ends.
On site the two stack. A stirrup at the large end of its tolerance, set on chairs at the low end of theirs, can leave less cover than you expect. Detailers allow for this by sizing stirrups and ties from the actual cover and form dimensions, and placers check cover with the bars tied. For the A23.1 side, see our guide to rebar placement tolerances.
When standard tolerances are not enough
Most work fits comfortably within standard tolerances. The cases that sometimes need more:
- Tight stirrups and ties in congested beams and columns, where a few millimetres decides whether the main bars fit.
- Precast and architectural concrete, where cover is small and visible.
- Bars that must fit embedded items, anchor plates or tight formwork.
- End-bearing compression splices, where bar ends are saw-cut square rather than sheared.
RSIC is clear on who decides: where greater accuracy is required than the standard figure, the engineer must clearly state it, and tighter tolerances are an extra charge. RSIC treats bending to more demanding tolerances, saw-cutting ends for compression splices and bending tighter than the recommended diameter as special fabrication, priced separately from ordinary bending. Put the requirement on the drawings before the bar lists are made, not on site after the bars arrive.
Checking bars on delivery
You do not need to measure every bar, but a quick check on the first bundles of each mark catches problems while they are cheap to fix:
- Check the tag first. Mark, size, grade and quantity should match the bar list and placing drawing.
- Measure a few bars per mark with a tape: overall length and the main legs, out-to-out.
- Check stirrups and ties against the size on the bar list, since they have the tightest tolerance.
- Look at the bends. Hooks should be at the right angle and a consistent shape; cracks at a bend are a reason to set the bar aside.
- Report problems right away. RSIC practice expects shortages to be reported promptly, and your supplier's terms will set a deadline. See how to order cut and bend rebar for the receiving routine.
If a bar is out of tolerance, talk to the fabricator before you fix it. Rebending on site is not always allowed: CSA A23.1 prohibits field bending of bars partly embedded in concrete unless the drawings show it or the engineer permits it, and some rebending can damage the bar. Our post on whether bending rebar weakens it covers the details.
A note on US tolerances
If you are reading American specifications, the Concrete Reinforcing Steel Institute (CRSI) publishes its own tolerance tables in inches, with values that vary by bar size and bar length. They are not a substitute for the Canadian values on a Canadian job, and they are written for US bar sizes. Our comparison of ACI and CSA detailing explains how the two systems differ.
Bar that fits the first time
Good tolerances start with a good bar list: accurate detailing, critical dimensions flagged and stirrups sized from the real cover. Procut details reinforcing steel from your structural drawings, then shears and bends 10M to 55M bar to the bar lists in our shop, tagged and bundled by mark.
Send us your drawings for a free take-off and quote, or see our services for detailing, fabrication and delivery.
Frequently asked questions
What is the standard tolerance for cutting rebar?
Under the RSIC Manual of Standard Practice, straight bars sheared to length are cut within plus or minus 25 mm, and the overall length of a bent bar is held within plus or minus 25 mm.
What is the bending tolerance for stirrups and ties?
Stirrups and ties are bent within plus or minus 13 mm on their leg dimensions. Spirals are held to plus or minus 13 mm on diameter below 750 mm and plus or minus 25 mm at 750 mm and larger.
How accurate does a 90 degree rebar bend have to be?
RSIC standard practice allows a maximum deviation of 2 degrees, or a slope of 1 in 23, on 90° bends.
Can I ask for tighter rebar tolerances?
Yes. The engineer has to state the requirement on the drawings, and the affected dimensions are flagged as critical on the bar list. Bending to tighter than standard tolerance is special fabrication and costs extra.
Is fabrication tolerance the same as placement tolerance?
No. Fabrication tolerance is how accurately the shop cuts and bends each bar. Placement tolerance, set by CSA A23.1, is how accurately the bars are positioned in the forms. The two add together on site.
