Charging Time Estimator by Vehicle Battery Size and Charger Level
Estimate how long it will take to charge your electric vehicle based on battery capacity, current and target state of charge, charger level, and charging efficiency.
Typical range: 85–95%. Accounts for heat loss during charging.
Formula
Step 1 — Energy Needed (kWh):
Energy Needed = Battery Capacity (kWh) × (Target SOC% − Current SOC%) ÷ 100
Step 2 — Effective Charger Power (kW):
Effective Power = Charger Power (kW) × (Efficiency ÷ 100)
Step 3 — Charging Time (hours):
Charging Time = Energy Needed ÷ Effective Power
Example: 75 kWh battery, 20% → 80% SOC, 7.2 kW charger, 90% efficiency:
Energy = 75 × (80−20)/100 = 45 kWh | Effective Power = 7.2 × 0.90 = 6.48 kW | Time = 45 ÷ 6.48 ≈ 6 hr 56 min
Assumptions & References
- Charging efficiency (85–95%) accounts for energy lost as heat in the onboard charger, cables, and battery management system. A default of 90% is used per SAE J1772 typical values.
- Level 1 charging uses a standard 120V household outlet at 12A continuous (per NEC 80% rule), delivering ~1.4 kW.
- Level 2 charging uses a 240V EVSE; power varies by amperage rating (16A–80A), delivering 3.3–19.2 kW.
- DC Fast Charging (DCFC) bypasses the onboard charger; power is delivered directly to the battery. Speeds of 50–350 kW are common (CHAdeMO, CCS, Tesla Supercharger).
- Most manufacturers recommend charging to 80% for daily use to preserve battery longevity (per Tesla, GM, and Nissan owner guidelines).
- Charging speed may taper above ~80% SOC for DC fast chargers; this calculator assumes a constant charge rate for simplicity.
- Range estimate uses an average of 3.5 miles/kWh, consistent with EPA combined ratings for mid-size EVs (e.g., Tesla Model 3, Chevy Bolt).
- References: SAE J1772 standard, U.S. DOE Alternative Fuels Data Center (afdc.energy.gov), EPA fueleconomy.gov.