Method for determining a volume V eff of a liquid medium, in particular a heated adhesive, effectively delivered to a consumer by a double acting, pneumatically driven piston pump, wherein the piston pump is subject to leakage, having the following features when a constant pressure is acting on a drive of the piston pump and at least one double stroke of the piston pump from one dead center position thereof to the other dead center position thereof and back to the first dead center position is carried out: a. without the piston pump being able to deliver the medium to the consumer, a leakage time t L auf for one stroke of the piston pump from the bottom dead center position thereof to the top dead center position thereof is measured, b. without the piston pump being able to deliver the medium to the consumer, a leakage time t L ab for one stroke of the piston pump from the top dead center position thereof to the bottom dead center position thereof is measured, c. a quotient of a volume of the medium V auf theoretically delivered by the piston pump without leakage and of the leakage time t L auf is determined for the stroke of the piston pump from the bottom dead center position to the top dead center position, d. a quotient of a volume V ab theoretically delivered by the piston pump without leakage and of the leakage time t L ab is determined for the stroke of the piston pump from the top dead center position to the bottom dead center position, e. the time t auf for the stroke of the piston pump from the bottom dead center position to the top dead center position and the time t ab for the stroke of the piston pump from the top dead center position to the bottom dead center position is measured as the medium is delivered to the consumer, f. the effectively delivered volume V eff is determined multiplied by the number of double strokes in accordance with V eff = V auf − V auf t L auf × t auf + V ab − V ab t L ab × t ab a. without the piston pump being able to deliver the medium to the consumer, a leakage time t L auf for one stroke of the piston pump from the bottom dead center position thereof to the top dead center position thereof is measured, b. without the piston pump being able to deliver the medium to the consumer, a leakage time t L ab for one stroke of the piston pump from the top dead center position thereof to the bottom dead center position thereof is measured, c. a quotient of a volume of the medium V auf theoretically delivered by the piston pump without leakage and of the leakage time t L auf is determined for the stroke of the piston pump from the bottom dead center position to the top dead center position, d. a quotient of a volume V ab theoretically delivered by the piston pump without leakage and of the leakage time t L ab is determined for the stroke of the piston pump from the top dead center position to the bottom dead center position, e. the time t auf for the stroke of the piston pump from the bottom dead center position to the top dead center position and the time t ab for the stroke of the piston pump from the top dead center position to the bottom dead center position is measured as the medium is delivered to the consumer, f. the effectively delivered volume V eff is determined multiplied by the number of double strokes in accordance with V eff = V auf − V auf t L auf × t auf + V ab − V ab t L ab × t ab