The objective of this study is to establish a feasible method for generating pressure-specific volume-temperature (PVT) data for thermoplastics on a microcomputer-controlled injection molding machine (IMM). This method utilizes the injection barrel of the IMM as a pressure chamber for determining the specific volume of thermoplastics at various pressure and temperature conditions. An empirical equation of state based on the Tait equation is used to fit the PVT data of three resins-low-density polyethylene (LDPE), polystyrene (PS), and acrylonitrile-butadiene-styrene copolymer (ABS). The comparison between LPDE’s PVT data generating from the IMM and from the classical bellows method indicated that the present method can be reasonably applied for determining the specific volume of thermoplastics as a function of pressure and temperature.