A drug delivery device comprises a housing and a dose sleeve located within the housing, the dose sleeve being configured to move helically within the housing as a medicament dose is dialled into or delivered from the drug delivery device. A dose setting arrangement is coupled to the dose sleeve and is configured to cause helical movement of the dose sleeve as a medicament dose is dialled into the drug delivery device through rotation of a dose dial forming part of the dose setting component. A dose delivery arrangement comprising a dose button is coupled to the dose sleeve and is configured to cause delivery of medicament with helical movement of the dose sleeve and without rotation of the dose dial when the dose button is actuated. A first sensor arrangement is configured for detecting a rotation of the dose dial relative to the housing. A second sensor arrangement is configured for detecting movement of the dose sleeve relative to the housing. A processor arrangement is coupled to receive inputs from the first and second sensor arrangements and is configured to calculate therefrom the size of a medicament dose dispensed by the drug delivery device.
