Although bubbly flows are encountered in Various engineering fields, there are very few established theoretical foundations on the interfacial area concentration, which have been supported by extensive experimental data. From this point of view, a simple equation for the interfacial area concentration under steady fully-developed bubbly flow condition has been derived from the interfacial area transport equation. The derived theoretical equation has been modified to obtain experimentally supported predictive correlation. The obtained interfacial area correlation was validated by 204 data sets measured in air-water bubbly flows under various conditions. These data sets covered extensive flow and loop conditions such as channel geometry (circular or rectangular channel), flow direction (vertical or horizontal flow), superficial gas velocity (0.018-4.87 m/s), superficial liquid velocity (0.262-6.55 mis) and interfacial area concentration (25.8-1083 m(-1)). An excellent agreement was obtained between the developed semi-theoretical correlation and data within an average relative deviation of +/- 11.1%.