Because of the number of variables that can affect range, such as ambient temperature, road conditions, vehicle specification, battery health and performance, state of charge, driving style and so on, it is better to consider what the typical energy consumption is, as you would look at the fuel consumption of a petrol or diesel car. Manufacturers do not typically quote consumption figures at given speeds, instead giving an overall figure according to the WLTP testing regime, but you can expect anything between 2.9 and 4.5 miles per kWh, again depending on the numerous variables. The actual range will depend on the consumption figure achieved applied to the state of charge of the battery and the capacity of the battery itself.