Rebar is unfinished steel reinforcing rod used to strengthen concrete. It comes in common lengths ranging from one-foot up to 20-feet and thicknesses of 1/2-inch or 5/8-inch. Rebar is placed directly into the concrete as part of the pouring process. One of the first steps in the concrete installation process is determining how much rebar will be needed for the job.

Rebar comes in many different lengths.

Step 1

Measure the size of the concrete foundation you will be installing. Run a tape measure across all the sides and add up the measurements for the total amount of linear feet. For a foundation that is 50-feet wide by 20-feet long, the total amount of linear feet would be 220 (50+50+60+60).

Step 2

Determine how far apart the concrete slabs will be. The slabs are the individual blocks or sections of concrete in the ground. Most slabs are 24 inches apart, while others can be 16 inches or eight inches apart. There must be one row of rebar for every eight inches of slab. For a 24-inch slab, three pieces of rebar will be necessary for each section.

Step 3

Multiply the total linear feet by three (following our example), since there will be three rows needed for each slab. In this case, 660 feet of rebar will be necessary for installation (220x3=660). The longest sections of rebar come in 20-foot lengths.

Step 4

Divide 660 by 20 for the number of pieces needed for installation of the concrete slab. This equals 33 20-foot pieces necessary for installation.