<p>Predicting the refining effect of ultrasonic melt treatment (UMT) on the solidification of metallic structures is usually tough, which hinders the use of UMT for industrial applications. Here, we present a numerical model for the accurate calculation of the cavitation volume during the UMT process in aluminum alloys. The accuracy of the model has been improved by incorporating the nonlinear propagation of ultrasound waves caused by the melt–bubble interaction. The consolidation of the model was completed through quantitative correlation between the crystal numbers and calculated cavitation volumes in a series of UMT experiments on a high-purity aluminum where the impurities and solute contaminants were excluded. We believe that this work can shed some light on quickly pre-measuring the UMT effect on engineering applications in aluminum alloys.</p>