How do I Choose the Best Rebar Sizes?

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  • Written By: G. Wiesen
  • Edited By: Heather Bailey
  • Last Modified Date: 26 November 2019
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To choose the best rebar sizes for a project, you should typically consider the use of the rebar in a particular job and the lengths of rebar you are going to need. There are different grades at which rebar is rated, and you should be sure to choose a grade that will sufficiently support the structure in which you are using it. You should also measure an area before you use rebar, especially for concrete pouring, to ensure you have proper sizes and bent pieces if necessary. As you consider the rebar sizes you need, you should also ensure you choose the proper thickness for your project.

Rebar, or reinforcing bars, are metal bars often used in construction, usually as a grid over which concrete is poured. There are many different sizes of rebar available, with different types of sizes referring to different properties of the rebar itself. Whenever you begin a project, you should consider the proper rebar sizes for different aspects of the project. One of the major ways in which rebar sizes are designated is by “grades,” which indicate the amount of weight the rebar is designed to support.

This grade is typically designated in both imperial units and metric units. The numeric designation indicates the minimum yield strength of the rebar. A grade 60 rebar, for example, uses imperial units and indicates that the minimum support of the rebar is 60,000 pounds per square inch (psi) or 60 kilo-pounds per square inch (ksi).


The same grade would be designated as 420 in metric units, representing a yield strength of 420,000 pascals (Pa) or 420 megapascals (MPa). Similarly, a grade 40 (280) rebar would have a minimum support strength of 40 ksi (280 MPa). It is important to choose the proper grade for rebar used in construction, and the American Society for Testing and Materials (ASTM) International provides standards for what grade should be used in various settings.

When choosing rebar sizes for pouring concrete, such as a driveway or porch, you should measure the space and determine the lengths of rebar you will need. Unless you have the proper equipment to cut rebar, you should be sure you do not buy rebar that is too long, since you can always connect pieces of rebar together using tie wire. You should also use bent pieces for corners, rather than connecting two pieces of rebar at a corner, as this can create a weak point in your concrete.

Proper rebar sizes can also be chosen based on the thickness of the rebar. This is also typically represented in both imperial and metric measurements. Imperial size designations indicate the thickness of the rebar in 1/8 of an inch. This means a #8 rebar is about 1 inch thick, while #3 rebar is only about 3/8 of an inch thick.

Thickness of rebar is indicated in metric units as the approximate diameter in millimeters (mm), rounded to the nearest 5mm. Rebar that is 11.3mm in thickness is designated as #10 rebar, and #20 rebar is often about 19.5mm in diameter. While you should follow construction codes in your area, you can typically use #3 (#10 in metric) rebar for driveways, #4 (#13) rebar for walls or columns, and #5 (#16) rebar sizes for foundation or building footings.


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Post 1

The correct way to choose rebar is in accordance with ACI 318. That and an engineering education are all you need to properly choose rebar.

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