EV range:
usable kWh ÷ kWh per 100 km × 100

How to estimate an EV's range

To estimate range, divide the usable battery energy by the consumption and multiply by 100. A 60 kWh battery at 18 kWh per 100 km gives 333.3 km. The answer is an estimate, because real consumption changes with every trip.

Two numbers go in. The first is the usable battery capacity in kWh, which can be a little lower than the headline figure the maker advertises. The second is the consumption in kWh per 100 km, which is the number you most need to get right.

EV range formula with worked examples

Find your own consumption figure

A brochure figure is measured under set test conditions, so your own number is more useful. Note the energy used on a trip from the car display or charger and divide by the distance. If a 70 km drive used 12.6 kWh, consumption is 12.6 ÷ 70 × 100 = 18 kWh per 100 km.

Use a figure from the kind of driving you will do. City driving, steady motorway cruising and hilly roads give quite different results, and so do the air conditioner, heater and a loaded boot. Fast motorway speeds generally raise consumption, which is why a range figure for a long trip is lower than one for town use.

Plan the trip with a reserve

Do not plan to arrive on an empty battery. A sensible approach is to keep a reserve, such as 10 percent, so a detour or a closed charger does not strand you. With 60 kWh and a 10 percent reserve, 54 kWh is available, and 54 ÷ 18 × 100 = 300 km.

For a longer drive, plan charging stops before you need them, and check that the charger on your route works with your car. A route that is 280 km long on a 300 km plan leaves little spare room if the weather turns cold or the traffic is heavy.

Using the estimate for daily driving

For a commuter, range is mostly a question of how often to charge. If you drive 40 km a day and the estimate is about 333 km, the battery covers over eight days of use, although most owners top up much sooner for convenience.

The estimate matters most on long trips, where charger spacing decides the route. Divide the trip into legs shorter than your reserve-adjusted range and look for a working charger at the end of each leg.

Common EV range mistakes

• Using the full battery size instead of the usable capacity.
• Mixing up kWh per 100 km with km per kWh. They are opposites.
• Using a gentle test figure for fast motorway driving.
• Forgetting that the real battery capacity falls as the battery ages.
• Counting on 100 percent charge, when most trips start at less.