# Rebar

> Rebar is steel bar cast into concrete to carry tension. US and metric rebar sizes, grades and coatings, typical cover, and what to check before the pour.

- URL: https://essential.construction/academy/glossary/rebar/
- Author: Kyle Parry (https://essential.construction/about-us/kyle-parry/, https://www.linkedin.com/in/kyleparry/) - Kyle Parry is the founder of Essential Construction. He has worked in construction for more than 20 years, leading projects across Canada for the country's largest contractors and developers.
- Publisher: Essential Construction (https://essential.construction/)
- Last updated: 2026-11-03

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**Rebar** (reinforcing bar) is a steel bar cast into concrete to resist tension, because concrete is strong in compression but weak in tension. Rebar is usually deformed with ribs so it bonds to the concrete, comes in standard sizes, and is placed in slabs, beams, columns, walls and footings to the engineer's drawings.

Rebar also controls cracking from shrinkage and temperature changes. On some sites it is called rerod or reinforcing steel.

## Rebar sizes (US)

US bar numbers are the nominal diameter in eighths of an inch up to #8.

| Bar size | Nominal diameter | Weight (lb/ft) |
| --- | --- | --- |
| #3 | 0.375 in | 0.376 |
| #4 | 0.500 in | 0.668 |
| #5 | 0.625 in | 1.043 |
| #6 | 0.750 in | 1.502 |
| #7 | 0.875 in | 2.044 |
| #8 | 1.000 in | 2.670 |
| #9 | 1.128 in | 3.400 |
| #10 | 1.270 in | 4.303 |
| #11 | 1.410 in | 5.313 |

Canada uses metric sizes such as 10M, 15M, 20M, 25M and 30M (about 11.3, 16.0, 19.5, 25.2 and 29.9 mm). The UK, Europe and Australia call bars by diameter in millimetres, such as 12 mm, often with a grade prefix on drawings.

## Grades and types

- **ASTM A615:** standard carbon-steel bar in the US; Grade 60 (60 ksi yield) is the most common.
- **ASTM A706:** low-alloy, weldable, more ductile; used in seismic design and where bars are welded.
- **Coated bars:** epoxy-coated and galvanized bars resist corrosion in parking decks, bridges and marine work.
- **Stainless steel and GFRP:** for severe exposure or where steel can't be used.
- **Elsewhere:** Canada uses CSA G30.18 (Grade 400W is common); the UK uses BS 4449 (B500B, B500C).

Bars carry rolled-on marks showing the producer, size, type and grade. CRSI publishes a bar identification guide.

## Placing rebar on site

Ironworkers place bars to the placing drawings and bar lists, set on chairs, bolsters or concrete blocks so the right cover is kept, and tie them with wire. Bars are joined with lap splices or mechanical couplers as detailed. Typical cover under ACI 318 for cast-in-place concrete:

- 3 in where concrete is cast against earth
- 1-1/2 to 2 in where exposed to earth or weather, depending on bar size
- 3/4 in for interior slabs and walls (#11 bars and smaller); 1-1/2 in for interior beams and columns

Canada (CSA A23.1) and other codes differ, and the drawings govern.

## Inspection before the pour

- Bar size, spacing and count match the drawings.
- Cover to forms and ground; chairs won't sink or tip.
- Lap lengths, hooks and couplers as detailed.
- Bars clean of mud, oil and loose rust; embeds and sleeves in place.
- Exposed bar ends capped or guarded against impalement (OSHA 1926.701(b) in the US).

## Related terms

- [Formwork](https://essential.construction/academy/glossary/formwork/)
- [Post Tension](https://essential.construction/academy/glossary/post-tension/)
- [Foundation](https://essential.construction/academy/glossary/foundation/)
- [Weld](https://essential.construction/academy/glossary/weld/)

## Related templates and guides

- [Rebar Takeoff](https://essential.construction/files/pre-construction/estimating/rebar-takeoff/)
- [Reinforcement Inspection Request Form](https://essential.construction/files/construction/quality/reinforcement-inspection-request-form/)
- [Concrete Pre-Pour Checklist Template](https://essential.construction/files/construction/quality/concrete-pre-pour-checklist-template/)
- [Concrete Formwork: Types, Design and Stripping Times](https://essential.construction/academy/tutorials/a-best-guide-to-formwork/)

## Frequently asked questions

### What is rebar made of?

Most rebar is carbon steel, often made from recycled scrap, rolled with ribs on the surface. Special types include low-alloy weldable steel, epoxy-coated or galvanized steel, stainless steel and glass fibre reinforced polymer (GFRP) for corrosive environments.

### What do rebar numbers mean?

In the US, the bar number is the nominal diameter in eighths of an inch for sizes up to #8, so a #4 bar is 1/2 inch and a #5 is 5/8 inch. Larger bars keep their numbers but don't follow the eighths rule exactly. Canada uses metric M sizes.

### Why is rebar ribbed?

The ribs, called deformations, lock the bar into the concrete mechanically. That bond lets tension pass between concrete and steel, so they act together. Plain smooth bar is rarely used for structural reinforcing today except for items like dowels that must slide.

### What size rebar is most common?

On houses and small buildings, #4 and #5 bars (or 10M and 15M in Canada) are very common in footings, slabs and walls. Larger buildings use bigger bars in columns, beams and mats. The structural drawings always set the size and spacing.