This article focuses on determining the friction factor from experimental results available in literature for gas flow in a smooth tube. The friction factor (f), Reynolds number (Re), and Knudsen number (Kn) are calculated from the reported pressure drop and mass flow rate. The variation in friction factor with Knudsen number and Reynolds number is analyzed in the Kn range of 0.0004-2.77 and Re range of 0.001-227. It is found that f Re is independent of gas and surface material and can be estimated by a simple semiempirical correlation within +/- 20% and a mean absolute error of 8%. The correlation gives friction factor for a particular value of Knudsen number and Reynolds number, irrespective of the type of gas or surface material.