Rebar Area Calculation
This article explains the difference between cross-sectional area calculations for plain round rebar and deformed rebar. An illustration of plain round bars (left) and deformed bars (right) are shown below.
For round plain rebar, the rebar diameter can be calculated simply as:
Steel Area, As = π*d^2 /4
For deformed rebar, the effective cross sectional area of the rebar including the ribs is slightly larger. However, for design calculation purposes, the difference is negligible. Therefore it is okay to use the simpler approximation for both plain and deformed rebar.