For the prediction of concrete performance, it is often beneficial to know the volume of pores in the concrete. ASTM C642-13 [Standard Test Method for Density, Absorption, and Voids in Hardened Concrete, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA] was originally introduced in 1969 as a “standard test method for density, absorption and voids in hardened concrete.” This technical note will compare the total pore volume (voids) obtained using ASTM C642-13 with that obtained using vacuum saturation for a typical bridge deck concrete. This technical note suggests that ASTM C642-13 may provide a consistent measure of the pores (voids) in the paste matrix of the concrete; however, it does not provide a measure of the total porosity that may be expected if all the pores in concrete are filled with water. Although an approach like ASTM C642-13 may be sufficient for some applications, the fact that it does not measure the total porosity should be considered by users of the test. This is important because this test method is being frequently applied to concrete durability and transport-related problems that require the total pore volume to be known.