Rebar, or reinforcing bar, is a bar that’s used to reinforce and strengthen concrete under tension. It’s typically made of steel, though fiberglass is popular for certain projects because it doesn’t corrode and is non-magnetic.
There are many steel rebar sizes, grades, and types to support a variety of structures. Standard rebar sizes can vary by country — metric size and imperial size are two popular measurements. In the United States, common specifications are published by the American Concrete Institute (ACI) and American Society for Testing and Materials (ASTM).
We’ll be focusing on different sizes of imperial bar, which are standard in the United States as outlined by ASTM A955/A955M Standard Specification for Deformed and Plain Stainless-Steel Bars for Concrete Reinforcement.
By better understanding what rebar is, how it is used, and the many variations and sizes available, you’ll have the confidence to work with this material for your next construction project.
Rebar Size Chart
Each imperial bar diameter increases by 1/8 inch. You can multiply the bar size by 1/8 to get the nominal diameter in inches. For example, #8 rebar = 8/8 inches (or 1 inch) in diameter. Common measurements indicate the weight, nominal area, and nominal diameter.
When working with rebar, it is imperative to understand not just the size of rebar you need, but also the grade and type of steel.
| Imperial Bar Size | Weight (lb/ft) | Weight (kg/m) | Nominal Diameter (in) | Nominal Diameter (mm) | Nominal Area (in2) | Nominal Area (mm2) |
|---|---|---|---|---|---|---|
| #3 | 0.376 | 0.561 | 0.375 | 9.525 | 0.110 | 71 |
| #4 | 0.688 | 0.996 | 0.500 | 12.700 | 0.200 | 129 |
| #5 | 1.043 | 1.556 | 0.625 | 15.875 | 0.310 | 200 |
| #6 | 1.502 | 2.240 | 0.750 | 19.050 | 0.440 | 284 |
| #7 | 2.044 | 3.049 | 0.875 | 22.225 | 0.600 | 387 |
| #8 | 2.670 | 3.982 | 1.000 | 25.400 | 0.790 | 509 |
| #9 | 3.400 | 5.071 | 1.128 | 28.650 | 1.000 | 645 |
| #10 | 4.303 | 6.418 | 1.270 | 32.260 | 1.270 | 819 |
| #11 | 5.313 | 7.924 | 1.140 | 35.810 | 1.560 | 1006 |
| #14 | 7.650 | 11.410 | 1.693 | 43.000 | 2.250 | 1452 |
| #18 | 13.600 | 20.284 | 2.257 | 57.330 | 4.000 | 2581 |
Here are common uses for each of the steel rebar sizes:
- #3 — This thin and cost-effective mild steel rebar material adds strength to concrete roads, driveways, or patios. It’s also common in poured concrete swimming pools to provide the pool walls with shape and strength.
- #4 — Slightly thicker, #4 rebar is perfect for adding strength to highways and can give columns and slabs added strength.
- #5 — This type of rebar is commonly used for bridges and highways.
- #6 — Commonly found in foundations, retaining walls, and roads or highways.
- #7 — This rebar size can provide support for structures like multi-story parking garages and bridges.
- #8 — #8 rebar is perfect for medium to heavy commercial applications. It can be used for slabs, sea walls, columns, and beams.
- #9 — This thick and durable material is the go-to rebar for high-rise construction projects, sea walls, and retaining walls.
- #10 — Perfect for medium to heavy commercial-use projects, this size provides structural support in beams, columns, and more.
- #11 — This heavy-duty rebar is thick and strong, so it is often used for load-bearing structures.
- #14 — One of the heaviest and thickest rebars available in standard sizes, the #14 rebar size is well suited for bridges, parking structures, tall buildings, and docks.
- #18 — This large, strong rebar size is used for large buildings, industrial facilities, and other large-scale buildings.
Rebar Grades
Understanding the difference between yield strength and tensile strength is necessary to evaluate what grade of rebar you need.
Think of yield strength and tensile strength as the minimum and maximum stress ranges for a particular rebar grade. Yield strength is the minimum amount of stress a material can take before it begins to deform permanently. Conversely, tensile strength measures the maximum amount of stress a material can take before being permanently damaged and broken.
Rebar grades are set by ASTM. The grade designation is equal to minimal yield strength in kilopounds per square inch (KSI). Common grades are 40, 60, 75, 80, and 100. The nomenclature for the grades represents how much yield the rebar has. For example, grade 40 rebar has a minimum yield strength of 40 KSI, which is equal to 40,000 PSI, whereas grade 80 rebar has a minimum yield strength of 80 KSI or 80,000 PSI.
Types of Rebar
Choosing the suitable rebar for your project will depend on the size and grade needed to add the necessary support and strength. It will also largely depend on the material used to make the rebar, as well as what’s used to coat it.
Carbon steel rebar is the standard in the concrete and construction industry, but it may not hold up well in high-moisture environments. An epoxy-coated rebar may work better in maritime applications, retaining the strength and durability of the concrete without accelerated corrosion.
Carbon Steel Rebar
Carbon steel rebar is the most common type of rebar used in residential and commercial projects. This alloy steel is exceptionally cost-effective and durable, but the carbon steel may not hold up well to projects with high moisture exposure. Using carbon steel rebar may be risky if you work with high moisture content or in high-humidity areas.
Stainless Steel Rebar
Although not as cheap as carbon steel rebar, stainless steel rebar can be a viable alternative. These steel reinforcing bars are used for bridges, roads, piers, and other weight-supporting structures. Unlike carbon steel rebar, stainless steel rebar can help prevent corrosion, giving you added protection.
Galvanized Rebar
One of the more expensive options, galvanized rebar, is an alloy steel rebar dipped in a zinc solution to add a special water coating that can deter corrosion. This material is an excellent alternative to epoxy-coated rebar. Galvanized rebar is 40 times more resistant to corrosion and holds up better during shipping and installation.
Glass Fiber Reinforced Polymer (GFRP) Rebar
Also known as fiberglass rebar, this material is perfect for projects that are exposed to water. Glass fiber rebar will never corrode and boasts a much greater tensile strength than traditional steel rebar. Plus, it’s 75% lighter than steel, which means you can save on costly shipping expenses. This specialized material also has non-conductive electrical properties.
Epoxy Coated Rebar
Epoxy-coated rebar works well in high-humidity and high-moisture construction projects. The rebar is coated with a thick epoxy, which helps to slow corrosion. Unfortunately, the delicate epoxy coating can become scratched and damaged during shipping, rendering the rebar much less effective against corrosion.
Welded Wire Fabric (WWF) Rebar
Although this type of material has a different kind of name than other standard rebar types, WWF rebar is actually a grid pattern made of welded low-carbon steel wire. The grid can help reinforce concrete slabs to improve the overall tensile strength of the concrete.
Expanded Metal Rebar
Similar to WWF rebar, expanded metal creates a metal mesh that is detailed in diamond-shaped lines. The mesh is made from a single steel sheet that is expertly cut and expanded. This material is commonly used when extremely thick plaster is needed to support the concrete. Expanded metal rebar is often used for sidewalks or walking surfaces, but it is not strong enough to withstand heavy vehicle traffic or heavy weights.
Conclusion
Rebar is an essential material for reinforced concrete. Choosing the proper size, grade, and type of reinforcement bars are crucial to the success of any project. Proper and even spacing is also important.
Fully understanding each rebar grade’s tensile and yield strength, as well as the benefits, disadvantages, and overall cost difference between your rebar options will allow you to create a safe, cost-effective, and durable project.
