The speed difference, worked out
Charging power is amps times volts. At the 240 volts a Level 2 circuit provides:
- 40 amps is about 9.6 kW. At our standard reference of roughly 3.5 miles of range per kWh, that is about 34 miles of range per hour.
- 48 amps is about 11.5 kW, or about 40 miles of range per hour.
So the gap is roughly six miles an hour, or about 18%. Across a ten-hour overnight window that is 340 miles against 400 — both of which are far more than any ordinary day of driving requires. If your daily driving is somewhere in the normal range, both chargers refill it in under two hours and then sit idle for the rest of the night.
We print the 3.5 miles-per-kWh assumption rather than a single flat number because your own car’s efficiency moves it. An efficient sedan will beat that figure; a large electric truck will fall well short of it. Substitute your own number and re-run the arithmetic — the ratio between 40 and 48 amps stays the same either way. Our how long to charge guide puts these rates against real battery sizes.
The circuit difference, and why it costs more
Here is the part the marketing skips. Under the National Electrical Code’s Article 625, EV charging is treated as a continuous load— a load expected to run at its maximum for three hours or more. Continuous loads are sized at 125% of the actual draw, which is the “80% rule” read the other way round.
Run that on both options and it lands on round numbers:
- 40 amps × 1.25 = 50 → a 50-amp circuit
- 48 amps × 1.25 = 60 → a 60-amp circuit
That difference has four consequences, and they compound.
Heavier wire. A 60-amp circuit needs larger conductors than a 50-amp one. Copper is priced by weight and the run to your garage may be long.
A bigger breaker, and space for it. Both are double-pole breakers, but a 60-amp one is a bigger demand on a panel that may already be close to full.
Ten more amps out of your service.This is the one that bites. An electrician does a load calculation on the whole house — range, dryer, air conditioning, water heater — and adds the charger. On a 100-amp service, the difference between finding 50 amps and finding 60 can be the difference between a routine job and a service upgrade, which is typically the largest single line on an EV charging quote.
No plug-in option.The common NEMA 14-50 receptacle is a 50-amp device, which is exactly why plug-in chargers cap at 40 amps of draw. Choose 48 amps and you are hardwiring, with everything that implies — see our hardwired vs plug-in comparison.
Our how many amps guide covers how to find out what your panel can actually spare, and our installation guide covers published cost ranges for the job. Note that the federal 30C credit that used to offset part of a home charger install has expired, so the install is a full-price line item now.
The trap: buying 48A and running it at 40
This happens constantly and it is worth naming. A 48-amp charger wired to a 50-amp circuit does not charge at 48 amps. It charges at 40, because that is what the circuit safely allows — and a correctly commissioned install will have it configured that way.
So if your panel gives you a 50-amp circuit and you buy a 48-amp charger, you have paid the 48-amp price for a 40-amp charging experience. You get the headroom only if you later upgrade the circuit, which is a real but uncertain future event.
There is one charger design that dodges this cleanly: adjustable amperage. The ChargePoint Home Flex sets its output anywhere from 16 to 50 amps in software, so you buy once, run at whatever your circuit allows today, and raise it if the circuit ever changes. If you are genuinely unsure which side of this comparison you are on, that adjustability is the answer to the uncertainty rather than a tiebreak on speed.
When 48 amps genuinely earns its keep
Four situations, and they are narrower than the marketing implies.
A large battery driven hard. An electric truck or large SUV with a big pack, regularly returning near empty, uses the extra rate. Six miles an hour compounds over a long charge: on a 300-mile refill it is roughly an hour and a half saved.
Two EVs sharing one charger. Two cars on one cable makes the overnight window suddenly finite. Our two-EV roundup covers this, along with load management, which is often the more useful feature than raw amps.
A short charging window. If your car is only plugged in from 10pm to 5am, or you have a time-of-use rate with a narrow cheap window, faster charging means more of your energy lands inside it. Our cost-to-charge guide has a calculator for what that is worth on your own rate.
A panel with obvious spare capacity. If 60 amps is genuinely free, the incremental install cost is small and there is no reason to leave the headroom on the table.
Outside those four, 40 amps is not a compromise. It is the sensible default, and it is why several of our favorite chargers — the Grizzl-E Classic Connect and the Lectron 40Aamong them — are 40-amp units and are none the worse for it.
What about 50 amps?
A few chargers, including the Autel MaxiChargerand the ChargePoint Home Flex at its top setting, go to 50 amps — about 12 kW, or roughly 42 miles of range per hour. In practice this also lands on a 60-amp circuit, because 50 × 1.25 = 62.5 and 60-amp breakers are what exists in the real world at that size. So 50 amps is a small bonus on top of the 48-amp decision rather than a third category: if you have the 60-amp circuit, take it; it does not change the install.
The verdict, by buyer
Choose 40 ampsif your panel is tight, if you want a plug-in charger you can take with you, or if your daily driving is comfortably inside an overnight window — which for most single-car households it is. You save on wire, on breaker, on load-calculation headroom, and often on the charger itself, for a difference you will rarely notice.
Choose 48 amps if your panel can genuinely spare a 60-amp circuit and one of the four situations above applies. In that case take it; the marginal install cost is modest when the capacity already exists.
Choose adjustable if you do not yet know. Buying a charger whose output you can set anywhere from 16 to 50 amps removes the need to guess, and future-proofs the purchase against a panel upgrade you might do in three years. That is the strongest argument for the Home Flex, and it is covered in full in our Emporia vs ChargePoint matchup.
