Charger listings advertise an amperage, and it's easy to assume that's the circuit you need. It isn't, and the gap between the two is where a lot of home charging projects go wrong.
The continuous load rule
Electrical code treats anything running at full draw for three hours or more as a continuous load, and EV charging is the textbook example — it can pull maximum current for hours at a stretch. Continuous loads must run on a circuit rated at least 125 percent of that draw.
So the arithmetic goes the other way from how people expect:
A 32 amp charger needs a 40 amp circuit. 32 × 1.25 = 40.
A 40 amp charger needs a 50 amp circuit. 40 × 1.25 = 50.
A 48 amp charger needs a 60 amp circuit. 48 × 1.25 = 60.
This is not an electrician being conservative. It's the code requirement, and it's what an inspector checks.
Why the biggest charger isn't the best choice
A 48 amp charger sounds better than a 40 amp one, and on paper it charges faster. But it needs a 60 amp circuit, and on a 100 amp service that is a very large share of everything you have — often more than what's actually available once the air conditioning, the range and everything else is accounted for.
Meanwhile, the practical difference overnight is frequently nothing at all. If your car is parked for ten hours and needs six hours of charging at the lower rate, the faster charger buys you time you were asleep for. Size the charger to your driving, not to the spec sheet.
Hardwired or plug-in
Chargers above 40 amps are generally hardwired rather than plugged in. Plug-in units on a 14-50 outlet are common at 32 to 40 amps and have the advantage that you can take the unit with you if you move. Both are fine when installed correctly; the choice is mostly about flexibility.
The load calculation is the real answer
None of the above tells you what your home can support. That comes from a load calculation against your existing service, and it's the step that determines whether you're looking at a straightforward circuit or a panel upgrade first. It's quick, and it's worth doing before you buy anything.
If your service can carry it, we'll install the circuit on permit and be done. If it can't, we'll tell you what it would take — before you've spent money on a charger that can't be installed.