What is the diameter of #3 rebar?

The diameter of #3 rebar is indeed 3/8 inch. The designation of rebar sizes is based on a numerical system where the number corresponds to the diameter in eighths of an inch. Thus, #3 rebar, being the third in the series, has a diameter of 3/8 inch (which is equivalent to 3 divided by 8). Understanding this sizing system is essential for contractors and builders, as it ensures the correct selection and use of rebar in concrete construction, contributing to the safety and integrity of structures. Other sizes of rebar, like #2 and #4, follow similar logic, leading to increased or decreased diameters of 1/4 inch and 1/2 inch respectively, but for #3, the diameter is definitively 3/8 inch.