Charger sizing is a routine-and-capacity question. Start with the energy required for typical driving, divide by the hours available to charge, then check that the electrical service can support the proposed continuous load.
Convert driving into energy
Daily charging energy is approximately daily miles ÷ vehicle efficiency. At 40 miles per day and 3.5 miles per kWh, the vehicle needs about 11.43 kWh before charging losses.
Worked example
With 10 available hours and 90% charging efficiency, required charger output is 11.43 ÷ 10 ÷ 0.90 = 1.27 kW. That is a small average requirement, although real-world margin may justify a higher-capacity unit for flexibility and recovery after longer trips.
Check headroom, not just vehicle demand
Existing household load, service capacity, load management, and the charger’s continuous rating all matter. A charger that fits the vehicle’s energy need may still exceed practical electrical headroom when ovens, HVAC, dryers, or other large loads operate.
When a smaller charger is better
Slower charging can reduce installation cost and demand on the service. Choose more capacity when the parking window is short, daily mileage is high, or recovery after a long trip matters. Have the final circuit design reviewed locally.
Sources
The figures and rules in this guide are checked against:
- Charging Electric Vehicles at Home — U.S. DOE Alternative Fuels Data Center
- Electric Vehicles — fueleconomy.gov (U.S. DOE / EPA)
- NFPA 70: National Electrical Code — National Fire Protection Association
- Wall Connector — Tesla Support