The question isn’t “how fast can my house charge” — it’s three questions stacked: what can the circuit deliver, what can the panel spare, and what can the car accept. The smallest answer wins, and it’s usually smaller than the marketing suggests.

The 80% rule, in one line

EV charging is a continuous load — it can run at full draw for hours — so code requires the circuit to be sized at 125% of the load. Equivalently: the EVSE’s current may be at most 80% of the breaker rating. That’s the entire rule; everything else is a lookup table:

Breaker	Max EVSE amps	Power @240 V	~Miles/hour*
15 A (120 V)	12 A	1.4 kW	~4
20 A	16 A	3.8 kW	~13
30 A	24 A	5.8 kW	~19
40 A	32 A	7.7 kW	~26
50 A	40 A	9.6 kW	~32
60 A	48 A	11.5 kW	~38
100 A	80 A	19.2 kW	~64

*at ~3.3 mi/kWh — scale by your car’s efficiency.

Two practical notes on the table: EVSEs are sold by their output amps (a “40-amp charger” wants a 50 A breaker, not a 40), and above 40 A output the hardware generally must be hardwired — plug-in tops out at the NEMA 14-50.

The car’s onboard charger is a cap too

The EVSE supplies AC; the car’s onboard charger converts it to DC — and that converter has its own rating, commonly 7.2, 7.4, 9.6 or 11.5 kW (a few vehicles reach 19.2 kW; many PHEVs sit at 3.3–7.2). A car with a 7.4 kW onboard limit sees zero difference between a 32 A and an 80 A EVSE. Before paying for capacity, look up “your model + AC charging rate” — the levels guide has the common ceilings.

Does the panel have room?

A 40–50 A circuit is roughly one electric dryer’s worth of load. Whether the panel can host it is a load calculation question — square footage, HVAC, water heater, range, existing big loads — not a breaker-count question. Broad strokes: a modern 200 A panel almost always fits a 40–50 A EVSE circuit; an older 100 A panel with electric heat, range and dryer is genuinely tight. Options short of a panel upgrade:

• Load-managed EVSEs throttle or pause charging when house demand peaks — often the difference between “fits” and “doesn’t.”
• Smaller circuit: a 20–30 A EVSE still refills most commutes overnight.
• Time-of-use scheduling: charging at 2 a.m. avoids coinciding with the house’s evening peak.

How much speed do you actually need?

Work backwards from miles: overnight hours × power × efficiency × (1 − ~12% losses). An 8-hour window on a 7.7 kW EVSE puts ~54 kWh into the pack — about 175–190 miles at 3.3–3.5 mi/kWh. If your worst day is 60 miles, a 24 A circuit covers it by midnight. If two EVs share the driveway, one 50 A circuit plus smart scheduling usually beats two 40 A ones.

Installation honesty

Budget for the circuit, not just the box: an EVSE runs $300–700, and installation ranges from a few hundred dollars (panel next to the parking spot, capacity to spare) to several thousand (long wire runs, trenching a detached garage, panel work). Many jurisdictions want a permit — take it; an inspected 60 A circuit is not the place to freestyle. Federal and utility incentives still offset EVSE and install costs in many areas — your utility’s EV page is the first place to check.

The short version: match the EVSE to the car’s AC limit, match the breaker to the EVSE at 125%, and let overnight hours do the work — most households land at 32–40 A and never think about charging speed again.

Frequently asked questions

Is 40 amps or 50 amps the better home charger circuit?

For most EVs, a 40 A breaker (32 A / 7.7 kW EVSE) is the sweet spot: it refills ~45–50 miles of range per hour, needs only common 8 AWG copper, and doesn't strain a typical panel. Go 50 A (40 A / 9.6 kW) if you drive big miles daily or have two EVs sharing time. Beyond that, check whether your car can even accept it — many cap at 7.4–11.5 kW AC.

Can I just plug into my dryer outlet?

Maybe, with caveats. A NEMA 14-30 (30 A dryer outlet) can feed a 24 A / 5.8 kW EVSE — but sharing the outlet with a dryer means swapping plugs, and old 3-wire NEMA 10-30 outlets lack a ground and are not safe for EVSE use without an electrician's review. A dedicated circuit is the clean answer.

Do I need a panel upgrade for an EV charger?

Often not. A 32–40 A EVSE adds roughly the load of an electric dryer; panels with spare capacity absorb it, and load-management devices can pause charging when the house peaks. A load calculation by an electrician is the deciding step — 100 A panels are tight, 200 A panels usually have room.

Plug-in or hardwired EVSE?

Plug-in (NEMA 14-50) is cheaper to install and portable — good up to 40 A continuous. Above 40 A the EVSE generally must be hardwired anyway; hardwired also removes a connection point that cheap receptacles can loosen over years of nightly plugging.

My car accepts 48 A — should I install 48 A?

Only if you'll use it: 48 A needs a 60 A breaker, heavier wire, and a hardwired EVSE — noticeably more cost for ~20% more power than a 40 A setup. If you arrive home near-empty on long days, it's worth it; if you refill 30 miles nightly, 32 A is silent overkill already.