EV Charge Rate Calculator
Calculate charging time, power (kW), and range added based on your electrical supply.
Total size of your EV battery.
Watt-hours per mile (lower is better).
120V (Standard) or 240V (Dryer/Level 2).
Usually between 12A and 50A for home.
Charging Analysis
Output Power (Theoretical):
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Energy Needed:
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Charging Speed (Range):
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Time to Charge:
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*Calculations assume ~90% charger efficiency and a linear charge curve. Charging speeds may slow down significantly above 80% SoC.
How to Calculate EV Charging Rate
Understanding the physics behind Electric Vehicle (EV) charging allows you to estimate exactly how long it will take to "fill up" your battery based on the power source available. Unlike gas stations where flow rates are standard, electrical outlets vary wildly in power delivery.
The core formula for EV charging power uses Watts Law:
Power (kW) = (Voltage (V) × Amperage (A)) / 1000
Inputs Explained
- Voltage (V): Electrical pressure. In the US, standard wall outlets are 120V (Level 1), while heavy appliances and dedicated EV chargers use 240V (Level 2). DC Fast Chargers utilize 400V or 800V architectures.
- Amperage (A): The volume of current flowing. A standard socket provides 12-15 Amps, while a dedicated home charger typically supplies 32 to 50 Amps.
- Battery Capacity (kWh): The size of your "fuel tank." Common sizes range from 40 kWh (Nissan Leaf) to 100+ kWh (Tesla Model S/X, Rivian).
- Vehicle Efficiency (Wh/mi): Similar to MPG. A lower number means the car is more efficient. An average sedan consumes about 250 Watt-hours per mile.
Common Charging Scenarios
Level 1 (Trickle Charging): Using a standard 120V outlet at 12 Amps yields roughly 1.4 kW. This adds about 3-5 miles of range per hour—suitable only for overnight charging if your daily commute is short.
Level 2 (Home Fast Charging): Using a 240V outlet at 32 Amps yields roughly 7.7 kW. This adds 25-30 miles of range per hour, easily recharging most EVs fully overnight.
The 80% Rule
This calculator estimates time based on a constant flow of power. However, once an EV battery reaches roughly 80% state of charge (SoC), the charging speed often drops to protect the battery health. This is particularly noticeable on DC Fast Chargers, but less of a factor for slower Level 1 or Level 2 home AC charging.