A machine (1) for sealing vacuum packs (100), comprising: a pump (3) for aspirating air from inside a pack (100); at least an electric motor (4) for actuating the pump (3), which electric motor (4) is destined to be powered by an electricity grid supply; at least a welding element (5) destined to be placed in contact with the pack (100), for welding and sealing the pack (100); a supply circuit (6) destined to connect the welding element (5) to the electricity grid supply; a control unit (7) destined to control the supply circuit (6) in order to supply electrical energy to the welding element (5); and measuring means (8) for measuring a value of a parameter indicating the electrical energy that the supply circuit (6) supplies to the welding element (5), which measuring means (8) are connected to the control unit (7), which control unit (7) is configured to determine the value of the electrical energy supplied to the welding element (5) from the start of the welding operation according to the measured parameter, and in order to interrupt supply of the electrical energy to the welding element (5) on reaching a predetermined value of the electrical energy.