There is provided a method for measuring in-situ the acoustic attenuation obtained by a hearing protection device worn by a user, comprising: positioning the hearing protection device comprising a microphone oriented towards the user's ear canal at the user's ear;positioning a cup-like measuring device comprising a loudspeaker oriented towards to user's ear and a microphone oriented towards to user's ear at the user's ear in such a manner that a closed space surrounding the hearing protection device is created by the measuring device; providing a test signal via the loudspeaker, capturing audio signals representative of the level of the test signal in the closed space by the microphone of the measuring device and capturing audio signals representative of the level of the test signal in the user's ear canal by the microphone of the hearing protection device; processing the audio signals captured by the microphone of the measuring device and the audio signals captured by the microphone of the hearing protection device and estimating the attenuation provided by the hearing protection device from the processed audio signals.