Rebar, or reinforcement bar, is used in construction to strengthen concrete. Rebar is made from steel and is covered in ridges, which help grip the concrete. Workers erect a rebar structure inside the concrete form using rebar held together with wire. Once the concrete is poured and cures, the rebar significantly increases the tensile strength of the concrete slab. Rebar comes in several sizes and is sized according to its diameter.

Building materials
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Rebar on construction site
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Construction worker attaches rebar at building site

Measure the diameter of the rebar in 1/8 inches.

Rust steel bars in construction site
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Rebar pile

The rebar is measured in increments of 1/8 inch. For example, if the rebar measures 3/8 of an inch in diameter, then the rebar size is three. A rebar with a 1 inch diameter would be a size eight. And 10/8 inch rebar would be size 10.

Rebar for Building
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Rebar and wood make-up flooring at building site

Measure the length of the rebar. In many home improvement stores, the rebar comes in lengths of 4, 10, and 20 feet. They will be listed by their size, or their diameter.