It is important to know the sound pressure signal at the eardrum in headphone reproduction and in audiological applications. Unfortunately, it is difficult to conduct direct measurement safely. Estimating pressure signals at the eardrum based on measurements done elsewhere in the ear canal is sensitive to positioning errors. This is particularly the case at the canal entrance. In addition, not knowing the acoustic properties of the ear canal makes estimation difficult. This study shows that when both sound pressure and velocity are measured at the canal entrance using a pressure-velocity probe, the pressure signal at the eardrum can be estimated with much higher accuracy than from the pressure-only measurement. The method is demonstrated and validated by using physical simulators and computational modeling.