Rebar strengthens concrete. Rebar-reinforced concrete is less likely to crack or break. When setting up the reinforcing bars of steel for your concrete project, you have to eventually connect two pieces of rebar. The point where rebar rods overlap is called a "splice." The local building code determines the amount of overlap required. The location of the rebar also affects the length of the splice. Footings, slabs and block walls have different rebar requirements. You can calculate the correct rebar splicing overlap by using basic maths.
Check the building regulations for the minimum required length of a rebar slice. For example, aim for a minimum overlap of 50 cm (20 inches) for horizontal rebar installations on a block wall.
Measure the size of your rebar. Your building code may determine the length of rebar splice based on size.
Multiply the size of your rebar times the number required by the county planning department. Many codes require the splice overlap for footings to be 30 times the diameter of the rebar. For example, a No. 4 rebar is 1.2 cm (1/2 inch) in diameter; 30 times 1.2 cm (1/2 inch) equals 36 cm (15 inches). Your rebar needs to overlap 37.5 cm (15 inches).