Skip to content
Volt & Cable

HUB 05 · Guides & Buying Advice

EV Charging Speed: kW vs Amps Explained

Amps, volts, kilowatts and miles per hour — the four numbers on every charging spec, and the simple math that connects them.

By Stephen V.Updated How we research
#ad

We earn a commission when you buy through our Amazon links, at no extra cost to you. It never affects our rankings, and we say so when the cheaper product is the better buy. How this works.

Charging speed is really about kilowatts (kW), but chargers are sold by amps. The bridge is one line of arithmetic: volts x amps = watts. A 40-amp charger on a 240-volt circuit is 9,600 watts, or 9.6 kW. Divide that into miles per hour and you get real charging speed — roughly 25–30 miles of range per hour for most EVs.

The one equation that matters

Power (watts) equals voltage times current (amps). So on a home 240-volt Level 2 circuit:

  • 32 amps x 240 V = 7.7 kW
  • 40 amps x 240 V = 9.6 kW
  • 48 amps x 240 V = 11.5 kW

That is why the amperage you chooseis just a proxy for kilowatts. A 120-volt Level 1 outlet at 12 amps is only about 1.4 kW — the same reason a wall outlet trickles so slowly.

From kW to miles per hour

A rough rule: most EVs travel 3–4 miles per kWh. So 9.6 kW adds roughly 28–38 miles of range in an hour, depending on the car's efficiency. Our charge-time guide turns that into full-charge hours for your battery size.

Why you may get less than the number

Two ceilings apply, and you get the lower of them: the charger's rating and the car's onboard AC charger. Plug a 48-amp charger into a car that only accepts 32 amps of AC and you charge at 32 amps. The circuit also matters — a charger can only pull what its breaker allows, per the wire size and breaker rules. DC fast charging is a different world, measured in tens or hundreds of kW; see DC fast charging explained.

The gear

Recommended gear for this guide

The products this guide refers to, with prices pulled live from Amazon and dated on each card.

  • Emporia Emporia Level 2 (48A)

    Most people who want the smart features too

    Emporia Level 2 (48A)

    The smart charger that does not charge a smart-charger premium — 48-amp capability and real energy monitoring for the price of a dumb one.

    $449.00Amazon
  • Lectron Lectron 40A Portable (Level 1/2)

    One charger for home and travel

    Lectron 40A Portable (Level 1/2)

    A dual-level portable with both a NEMA 14-50 and a 5-15 plug — the take-it-anywhere charger that also covers a wall outlet in a pinch.

    Check price on Amazon →

#ad · As an Amazon Associate we earn from qualifying purchases.

Questions

Frequently asked

How do I convert amps to kW for charging?
Multiply amps by volts and divide by 1,000. On a 240-volt home circuit, 40 amps is 9.6 kW; 48 amps is 11.5 kW. That kW figure is what actually sets your charging speed.
How many miles per hour does a home charger add?
Roughly 25–30 for a typical EV on a 40–48A Level 2 charger, based on 3–4 miles per kWh. Efficient cars gain more; heavy trucks and SUVs gain less.
Why is my car charging slower than the charger's rating?
You always get the lower of the charger's limit and the car's onboard AC charger limit. If your car accepts only 32 amps, a 48-amp charger still delivers 32.

Keep reading

Related

Receipts

Sources

We do not run a testing lab, and we do not pretend to. Where a measured number came from someone else's lab, we name them and link them. Where we could not verify something, we say so on the page rather than quietly leaving it out. Read our full method.