In 1949 the authors undertook an investigation dealing with the design of asphaltic concrete mixes. The work was of such nature that accurate per cent density determinations were highly desirable. Shortly after the work was started per cent densities were obtained which exceeded 100 per cent, using bulk specific gravity for the aggregate. Use of the apparent specific gravity gave densities which were obviously too low. In an effort to obtain more accurate results, a method was developed and employed termed the “effective specific gravity.” Briefly, it is determined as follows: An asphaltic concrete specimen is made up with sufficient asphalt cement to overfill the voids in the compacted aggregate. The specific gravity of the molded specimen is obtained by the water immersion method. If the specific gravity of the asphalt cement is not known, it is determined by the pycnometer method. The effective specific gravity, g_e, is calculated by means of the following equation: ge=100−Wa100Ge−Waga...........(1) where: g_e = effective specific gravity of aggregate in specimen at 77 F, G_e = specific gravity of molded specimen with voids overfilled, g_a = specific gravity of asphalt at 77 F, and W_a = asphalt cement in specimen, per cent by weight.