EV Charging Calculator

How long does it take to charge an EV? It depends on your battery size, charger power, and how much charge you need.

Our EV charge time calculator uses the formula: Time = Battery kWh × Charge% / (Charger kW × Efficiency).

Compare for your specific vehicle:

• Level 1 (40+ hours)
• Level 2 (4-10 hours)
• DC Fast (20-60 minutes)

Calculate exactly how much it costs to charge your electric vehicle at home or at a public station.

Our EV charging cost per kWh calculator multiplies your energy usage by your electricity rate, accounting for efficiency losses.

Compare home charging vs public DC fast charging to find the most economical option.

• Level 1 (120V, 1.4 kW) is free to install but painfully slow.
• Level 2 (240V, 7-19 kW) is the home charging sweet spot.
• DC Fast (50-350 kW) is for road trips.

Our calculator compares all three charger types side by side, showing time and cost differences for your specific EV battery size.

EV charge time is the energy you need divided by the effective power delivered: Charge Time (h) = [Battery Capacity (kWh) × (Target% − Current%) / 100] / (Charger Power (kW) × Efficiency).

Because power in kilowatts equals energy in kWh per hour (kW = kWh/h), dividing energy by power yields time in hours.

For a 75 kWh pack charging 20% → 80%, energy into the battery is 75 × 0.60 = 45 kWh; at 7.7 kW and 90% efficiency, time = 45 / (7.7 × 0.90) = 45 / 6.93 ≈ 6.5 hours.

This linear model matches the U.S. Department of Energy's charging guidance for AC Level 1 and Level 2.

Charging uses two SI-derived electrical units:

• the kilowatt-hour (kWh) for energy
• the kilowatt (kW) for power

Per NIST and the BIPM SI system, one watt equals one joule per second, so 1 kWh = 3.6 megajoules (1000 W × 3600 s).

Power relates to voltage and current by P = V × I, giving watts from volts and amperes. A 240 V Level 2 circuit drawing 32 A delivers 240 × 32 = 7,680 W ≈ 7.7 kW.

Battery capacity and energy consumed are billed in kWh, while charger output and charge rate are quoted in kW.

Charging cost is simply the energy drawn from the grid times your electricity rate: Cost = Energy (kWh) × Rate ($/kWh), where Energy = Battery kWh × Charge% / Efficiency.

Charging a 75 kWh pack 20% → 80% draws 45 / 0.90 = 50 kWh; at $0.14/kWh that is 50 × 0.14 = $7.00.

To get cost per mile, divide by miles added: if efficiency is about 3.5 miles per kWh, 45 usable kWh adds ~157 miles, so $7.00 / 157 ≈ $0.045 per mile.

The EPA fuelEconomy.gov database publishes per-model miles/kWh figures to refine this estimate.

Charging power follows Ohm's law and the power relation P = V × I, so raising either voltage or current increases kilowatts delivered.

• Level 1 uses a 120 V outlet at roughly 12 A ≈ 1.4 kW.
• Level 2 uses 240 V at 16–80 A, giving about 3.8–19.2 kW.
• DC fast charging bypasses the onboard AC-to-DC converter and pushes 400–1000 V directly to the battery, reaching 50–350 kW.

Per IEEE and IEC 61851 charging standards, a car's real intake is capped by its onboard charger (AC) or battery limit (DC), so a 7.7 kW car cannot charge faster on an 11 kW station.

Not all grid energy reaches the battery: some is lost as heat in the cables, onboard charger, and cells, described by charging efficiency (η).

Grid energy = battery energy / η, so lower efficiency means you pay for more kWh than you store.

Level 2 AC charging is typically 85–95% efficient, while cold weather, battery thermal management, and very low charge rates push losses higher.

HyperPhysics (Georgia State University) explains that resistive I²R losses rise with current, which is why trickle Level 1 charging can be proportionally less efficient than a well-matched Level 2 setup.

Drivers use these calculations to:

• plan overnight home charging
• budget road trips
• compare utility tariffs

Estimating charge time helps decide whether a 240 V Level 2 install is worth it versus a standard outlet, and cost-per-kWh math reveals when off-peak rates or a home solar array pay off.

Fleet managers apply the same P = V × I and energy formulas to size depot chargers and forecast electricity bills.

Encyclopaedia Britannica notes electric vehicles' higher tank-to-wheel efficiency versus combustion engines, which the per-mile cost output makes concrete for real budgets.

DC fast charging is not linear: chargers deliver peak power at low state of charge and taper sharply near 80% to limit heat and protect lithium-ion cells.

This means the simple linear time formula overestimates speed for the final 20%, and the last stretch to 100% can take as long as 20% → 80%.

For accurate road-trip planning, treat 10% → 80% as the fast window and expect diminishing returns beyond it.

Khan Academy's electrochemistry lessons explain how rising internal resistance and lithium-plating risk near full charge force this reduced current.

• The most frequent error is ignoring efficiency and using battery kWh directly, which understates both time and cost by 5–15%.
• Second, assuming the car charges at the station's rated power — a 7.7 kW onboard charger caps AC intake regardless of a larger charger.
• Third, applying the linear formula above 80% on DC fast charging, where tapering dominates.
• Fourth, mixing units, such as multiplying kW by minutes instead of hours (recall 1 kW × 1 h = 1 kWh, per NIST).
• Finally, forgetting cold-weather losses, which can cut charging speed and efficiency by 10–30%.