How EV charging time is calculated
Multiply the battery size by the percentage you want to add to get the energy stored. Some energy is lost as heat in the charger and battery, so the energy drawn from the grid is higher. Divide by the charger power for the time, and multiply by your rate for the cost.
Example: 75 kWh battery, 20% to 80%, 40 A Level 2
75 × 60% = 45 kWh added, or 50 kWh from the grid at 90% efficiency. 50 ÷ 9.6 kW = 5 h 13 min. At $0.17/kWh it costs $8.50 and adds about 158 miles at 3.5 mi/kWh.
Charger levels
| Type | Power | Miles of range per hour* |
|---|---|---|
| Level 1 (120 V outlet) | 1.2–1.9 kW | 4–6 |
| Level 2, 32 A | 7.7 kW | ≈ 24 |
| Level 2, 48 A | 11.5 kW | ≈ 36 |
| DC fast charger | 50–350 kW | 150–1,000 |
* At 3.5 mi/kWh and 90% efficiency. The car's onboard charger may limit Level 2 power.
Frequently asked questions
How long does it take to charge an EV at home?
On a 40 A Level 2 charger, most EVs charge from 20% to 80% in about 4–6 hours. On a standard 120 V outlet it can take 1–2 days.
Why does fast charging slow down after 80%?
The car reduces current to protect the battery as it fills, so the last 20% takes about as long as the first 60%.
What size breaker does a Level 2 charger need?
A 48 A charger needs a 60 A circuit, and a 40 A charger needs a 50 A circuit, because EV charging is a continuous load (125% rule).