Electric Vehicle Charger Calculator
Calculates Level 2 residential electric vehicle supply equipment (EVSE) charging rates in miles of range added per hour, continuous electrical load calculations (80% rule under NEC Article 625), circuit breaker sizing (40A, 50A, 60A), copper wire gauge (6 AWG vs 4 AWG), and charging costs.
Formula
Charge kW = (Amps × 240V) ÷ 1000; Charge Time = (Miles ÷ 3.5 mi/kWh) ÷ kW; Wire Gauge = (50A: 6/3 Romex NM-B; 60A: 6 AWG THHN)
1. Continuous Current Rating (NEC 80% Rule): 50A Breaker = 40A Continuous; 60A Breaker = 48A Continuous 2. Power Output (kW) = (Continuous Amps × 240 Volts) ÷ 1,000 3. Charging Speed (Miles/Hour) = Power kW × 3.5 miles/kWh (average EV efficiency) 4. Daily Recharge Time (Hours) = Daily Miles ÷ Charging Speed (Miles/Hour) 5. Copper Wire Spec: 50A = 6/3 NM-B Romex; 60A = 6 AWG or 4 AWG THHN in conduit 6. Monthly EV Fuel Cost = (Daily Miles × 30 days ÷ 3.5 mi/kWh) × $0.16/kWh
Inputs
- Average Daily Commute Mileage
- Level 2 EV Charger Circuit Size
- Distance from Electrical Panel to Garage Wall (feet)
Worked example
Installing a 50-amp NEMA 14-50 circuit with 35 feet of 6/3 Romex wire.
Outcome: Charges at 32 miles of range per hour (9.6 kW). Completely recharges the 40-mile daily commute in just 1.25 hours overnight. Requires a 50-amp 2-pole breaker, 40 feet of 6/3 NM-B copper Romex wire, and a commercial-grade NEMA 14-50 receptacle. Monthly electricity fuel cost: ~$55/month.
Why does a 48-amp EV charger require a 60-amp circuit breaker and hardwiring?
The NEC 80% continuous load rule states a breaker can only carry 80% of its rated capacity for continuous loads (48A ÷ 0.80 = 60A). Furthermore, plug-in NEMA receptacles are only rated up to 50 amps, meaning any charger drawing 48 amps must be directly hardwired into the electrical junction box.