Curb weight (American English) or kerb weight (British English) is the total mass of a vehicle with standard equipment and all necessary operating consumables such as motor oil, transmission oil, coolant, air conditioning refrigerant, and sometimes a full tank of fuel, while not loaded with either passengers or cargo.
This definition may differ from definitions used by governmental regulatory agencies or other organizations. For example, many European Union manufacturers include the weight of a 75-kilogram (165 lb) driver to follow European Directive 95/48/EC. Organizations may also define curb weight with fixed levels of fuel and other variables to equalize the value for the comparison of different vehicles.
The United States Environmental Protection Agency regulations  define curb weight as follows: Curb weight means the actual or the manufacturer’s estimated weight of the vehicle in operational status with all standard equipment, and weight of fuel at nominal tank capacity, and the weight of optional equipment computed in accordance with §86.1832–01; incomplete light-duty trucks shall have the curb weight specified by the manufacturer.
Unladen mass depends on the manufacturer and can be the same as curb weight, however, it is often the total mass of the car without a driver, fluid or any additional equipment.