In the UK the accepted ‘norm’ for measuring the efficiency of electric cars is 'miles per kWh'. The amount of electrical power stored in the batteries of an electric car is measured in kilowatt hours – or kWh for short. More efficient electric cars will be able to go further on each kWh, in the same way that an economical petrol car will be able to go further on a gallon of fuel than an uneconomical one. To find out more read our advice guide Miles per kWh: EV efficiency explained