EV Charging Calculator
How long an electric car takes to charge, the energy it takes from the grid and what it costs, from the battery size, charge levels and charger power.
Result…
How it's calculated
Energy added = battery × (target % − start %) From the grid = energy added ÷ efficiency Time = energy from the grid ÷ charger power Cost = energy from the grid × price per kWh · Range = energy added × distance per kWh
The battery size is the usable capacity in kWh, and the charge levels are the percentages on the car's display. Some energy is lost as heat in the charger and battery, so the grid supplies more than the battery receives: at 90% efficiency, 36 kWh into the battery takes 40 kWh from the grid, and that is the figure you pay for. The time assumes the charger power stays the same throughout, which is close for slow home charging but not for rapid charging, which tapers off as the battery fills. The range uses the car's own distance per kWh, which changes with speed, temperature and heating or cooling.
Your numbers, step by step
About the EV Charging calculator
This EV charging calculator shows how long an electric car takes to charge from one battery level to another, how much energy that takes from the grid, and what it costs at your price per kWh. Enter the usable battery size, the charge now and the charge you want, the charger power and a charging efficiency, because some energy is lost as heat and you pay for what comes from the grid, not what reaches the battery. Add your car's distance per kWh in kilometres or miles and it also shows the range added and the cost per 100 km or miles. It is useful for planning an overnight charge at home, comparing a wall box with a rapid charger, or checking a public charging price. The working is shown step by step. Real charging is often slower near full, so treat the time as the shortest it could take.
How to use it
- Enter the “Usable battery size” in kWh from the car's specifications.
- Set “Charge now” and “Charge to” as percentages from the car's display.
- Enter the “Charger power” in kW, the lower of the charger's rating and what the car accepts, and a “Charging efficiency”.
- Enter the “Price per kWh” you pay at home or at the charger.
- Optionally add the “Car's efficiency (optional)” and choose km or miles per kWh to see the range added.
Worked example
A car with a 64 kWh usable battery charges from 15% to 80% on a 7 kW home charger at 90% efficiency. The battery gains 64 × 65% = 41.6 kWh, which takes 41.6 ÷ 0.9 = 46.22 kWh from the grid. At 7 kW that is 46.22 ÷ 7 = 6.6 hours, or 6 h 36 min. At 0.25 per kWh it costs 46.22 × 0.25 = 11.56. At 6.5 km per kWh the charge adds about 270 km of range, about 4.27 per 100 km.
Updated
Questions people ask
How do I calculate EV charging time?
Multiply the battery size by the percentage you add to get kWh, divide by the charging efficiency to get the energy from the grid, then divide by the charger power in kW. The answer is in hours.
How much does it cost to charge an electric car?
The energy from the grid times your price per kWh. Because of charging losses, that is more than the kWh the battery gains. Public chargers may add session or time fees on top, which this does not include.
Why does charging slow down above 80%?
Cars reduce the charging power as the battery fills to protect it, and the effect is strongest on fast DC chargers. That is why rapid charging is often quoted to 80%, and why the last part of a charge takes longer than this calculator shows.
Why does my car charge slower than the charger's rating?
The car's onboard charger or battery may accept less power than the charger offers, and a cold battery charges more slowly. Enter the lower of the two powers for a closer estimate.
What charging efficiency should I use?
It depends on the car, the charger and the conditions, so a measured figure is best: compare the kWh your meter or charger reports with the kWh the car says it gained. The calculator starts at 90% as an example. The electricity cost calculator prices other appliances the same way.