Amps, Volts, kW: EV Charging Speed Explained Without the Engineering Degree
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Charger shopping is overwhelming because everyone throws around numbers, 40 amps, 48 amps, 9.6 kW, 11.5 kW, and nobody explains what they actually mean for your daily life. Let me translate all of it into one thing that matters: how many hours until your car is full.
The Three Numbers That Matter
Volts (V): Think of this as water pressure. Your standard household outlet is 120V. Your dryer outlet is 240V. Higher voltage means electricity pushes harder, which means faster charging. Level 2 chargers use 240V. That's why they're 4-6x faster than Level 1.
Amps (A): Think of this as the pipe diameter. More amps means more electricity flowing at once. A 32-amp charger lets less electricity through than a 48-amp charger, even at the same voltage. This is the spec that varies most between Level 2 chargers.
Kilowatts (kW): This is the actual speed. It's volts times amps, divided by 1,000. A 240V charger at 48 amps = 11.52 kW. This number tells you how fast energy flows into your battery.
240V x 32A = 7.68 kW
240V x 40A = 9.6 kW
240V x 48A = 11.52 kW
Higher kW = faster charging. That's the entire concept.
From kW to Hours: The Calculation You Actually Need
ChargePoint Home Flex Level 2 EV Charger (50A)
Adjustable 16-50A, 240V, J1772, NEMA 14-50 plug or hardwire, the universal smart charger that works with every non-Tesla EV.
See on Amazon →Your car's battery size (in kWh) divided by your charger's speed (in kW) equals charging time. Simple division.
Example: Tesla Model 3 has a 60 kWh battery. Charging from 20% to 80% means adding 36 kWh (60% of 60 kWh). With an 11.5 kW charger: 36 / 11.5 = 3.1 hours. With a 7.7 kW charger: 36 / 7.7 = 4.7 hours.
For daily driving, you're rarely charging from empty. If you drive 40 miles and your car gets 3.5 mi/kWh, you need about 11.4 kWh, roughly one hour on a 48-amp charger, or 1.5 hours on a 32-amp charger.
Common Charger Speeds Compared
| Charger Type | kW | Mi/Hour | 0-100% (60kWh) |
|---|---|---|---|
| Level 1 (120V/12A) | 1.44 | 4-5 | ~42 hours |
| Level 2 (240V/16A) | 3.84 | 12-14 | ~16 hours |
| Level 2 (240V/32A) | 7.68 | 25-28 | ~8 hours |
| Level 2 (240V/40A) | 9.6 | 30-35 | ~6.5 hours |
| Level 2 (240V/48A) | 11.52 | 35-44 | ~5.5 hours |
The Catch: Your Car Limits the Speed
Here's what charger companies don't emphasize: your car has a maximum onboard charger that caps how fast it can accept AC power, regardless of what your wall charger delivers.
Most modern EVs have 7.7 kW or 11.5 kW onboard chargers. Some (like certain Hyundai/Kia models) have 11 kW. Teslas range from 7.7 kW to 11.5 kW depending on model and configuration. Check your specific vehicle.
Do You Need 48 Amps?
If your car can accept 11.5 kW (48 amps at 240V), a 48-amp charger maximizes your speed. If your car tops out at 7.7 kW, a 32-amp charger delivers the same real-world speed at a lower cost.
That said, a 48-amp charger future-proofs you. Your next EV might have a faster onboard charger. The price difference between a 32-amp and 48-amp wall charger is typically $50-$100, worth it for the flexibility.
Drive less than 40 mi/day? Any Level 2 charger works.
Drive 40-80 mi/day? 32-amp or higher is comfortable.
Drive 80+ mi/day or have a large battery? 48-amp gives the best overnight recovery.
Not sure? Get a 48-amp charger. You'll never wish you had less speed.
⚡Disclaimer: This article is for informational purposes only. Smart home installations may involve electrical wiring and must comply with local building codes. Electrical work should only be performed by a licensed electrician.
Published by the Smart EV Home Charger editorial team. Published June 22, 2026.
Editorial responsibility: see Imprint.
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