Air permeability was determined for concretes of variable porosity (w/c ratio of 0.33, 0.50, and 0.67). The reproducibility of the test and the ability to characterize the permeability of different concrete were evaluated. Results indicate that air permeability test gives suitable reproducibility with a margin of error of 10%, which tends to improve with increase in w/c ratio. The difference in air permeability of concretes with the w/c ratios investigated are distinguishable by this technique. Furthermore air permeability coefficients used were modified with equations derived in accordance to Darcy's law, and the resulting air permeabilities compared. Data calculated with an air permeability coefficient based on mean radius pore (corrected equation) appears to give a more realistic value with greater differentiation between the ranges. Values were determined on specimens after 28 days, maintained at room temperature (50% RH), then again after an additional 2 days at 60°C in a ventilated oven. Oven-dried specimens exhibit significantly greater air permeability.