A methodology is presented to estimate cavity melt temperatures and part weight in the injection molding of amorphous thermoplastics. The approach uses measurements of cavity pressure near the gate and surface temperatures at three sensor locations. The surface temperature data with a heat conduction model give estimated temperature profiles across the cavity thickness. These profiles are then used to estimate the average cavity melt temperature. Fitting the cycle-to-cycle values of average mold-cavity temperature and peak pressure to a Tait equation yields a model to estimate part weights. The estimated part weights agree with measured values for different injection-molding conditions.