A method of estimating an acoustic transfer quantity representative of a sound pressure transfer to the eardrum includes the steps of measuring, by an ear canal microphone of the hearing instrument, an acoustic signal in the ear canal when a sound signal is emitted into the ear canal by a receiver of the hearing instrument, the ear canal microphone being in acoustic communication with the ear canal, determining, from the acoustic signal and from a frequency dependent reference characteristics of the hearing instrument, an ear canal impedance, and, calculating, from the ear canal impedance, an estimate of the acoustic transfer quantity.
