A dose counting mechanism for indicating the quantity of dosage available within a metered dose inhaler having a canister with an aerosol fluid and a housing body for housing the canister, wherein a wall of the housing body includes formations to support a resilient element, a wheel formation, a elongate threaded element, and a threaded formation including a pointer. The depressing of the canister to release aerosol fluid displaces the resilient element which engages with the wheel formation to rotate the wheel formation. The elongate threaded element engages with the wheel formation such that the rotation of the wheel formation causes rotational movement of the elongate element. The threaded formation engages with the elongate element whereby the rotational movement of the elongate element causes the linear displacement of the threaded formation and the pointer, whereby the position of the pointer indicates the quantity of fluid within the canister.