EV Charging From a Generator: Honest Calculator

Data reviewed 2026-07-05 ·how we calculate

Yes, a generator can charge an electric car — and this page exists to show you exactly how slowly, because EV charging is where generator marketing and physics part ways. A Level 1 charger draws a modest 1,440W that many portables supply easily, but at that rate a typical EV gains only 3–5 miles of range per hour. Level 2 charging needs 240V and 7,700W or more, continuously, for hours. The calculator gives real numbers for both; the FAQ does the miles-per-gallon-of-generator-gas math that decides whether it’s ever worth it.

Size a generator for this load

Computed on typical values; ranges shown below. 25% headroom applied.

Generator safety — read every time

Never run a generator indoors, in a garage, or near windows, doors or vents.Carbon monoxide kills quickly and without warning — place the generator 20+ feet from the house with the exhaust pointed away, and use battery CO detectors inside.
Never backfeed your house through a wall outlet or dryer outlet. Backfeeding can electrocute utility line workers and destroy equipment when power returns.
Connecting a generator to home circuits requires a transfer switch or interlock installed by a licensed electrician. There is no safe DIY shortcut, and this site does not provide wiring instructions.
Use heavy, outdoor-rated extension cords (12-gauge or thicker), fully uncoiled, sized to the load and the distance.

How to size it step by step

For emergency Level 1 charging: set the EV cord to its lowest amp setting first (often 8A), plug into a ground-bonded inverter generator of 2,000W+, and expect 3–5 miles of range per hour at 12A.
Apply the headroom rule as usual: 1,440W × 1.25 = 1,800W — but remember this is continuous for hours, so a generator that "fits" will run near its continuous rating the whole time. Bigger is genuinely better here.
For Level 2: the generator must supply 240V and hold 7,700W+ continuously — that is a 9,000–12,000W portable at minimum, run hard for hours. At that point compare the fuel cost honestly against driving to a working charger.
Check your EV’s requirements: some models refuse charging from floating-neutral generators. A grounding/bonding plug on the generator (installed per its manual) resolves it for many models — consult the EV manufacturer, not forum folklore.

Pro tips

Check your nameplate first — every figure on this page is a planning estimate, and the label on your specific unit beats any chart.
If you must generator-charge, do it at the EV cord’s lowest amp setting: gentler on the generator, and the efficiency penalty of running the engine lightly loaded is smaller than a stall mid-session.
Preconditioning (heating/cooling the cabin) while generator-charging can consume most of what the generator delivers — leave climate off until you unplug.

The data behind this calculator

EV charging loads and what they actually deliver
Figure	Value	Source
Level 1 draw (120V, 12A)	1,440W continuous	SAE J1772; EVSE cord specifications
Level 1 charging speed	~3–5 miles of range per hour	DOE Alternative Fuels Data Center Level 1 guidance
Level 2 draw (240V, 32A example)	7,680W continuous (16–48A units: 3,800–11,500W)	SAE J1772; ChargePoint/Tesla Wall Connector specs
Gasoline-to-range efficiency via generator	very roughly 8–15 miles per gallon of generator fuel	Arithmetic: ~2–3kWh/gal delivered × 3–4 mi/kWh, charging losses included — estimate, verify

Duty cycle: Unlike every other load on this site, EV charging is continuous for hours at full draw — the generator runs at high load the entire session, so fuel consumption and duty ratings matter more than surge.

EV charger generator questions, answered

Can a portable generator charge an electric car?

Yes, with the right expectations. A Level 1 cord draws 1,440W at 12A — with 25% headroom, 1,800W, so even a 2,000W inverter class generator technically suffices — but delivers only 3–5 miles of range per hour. Overnight on a generator gets you roughly 30–50 miles. It works as an emergency measure; as a routine strategy it is one of the least efficient ways to move a car ever devised.

How big a generator do I need for Level 2 EV charging?

A 32A Level 2 unit draws 7,680W at 240V, continuously — with headroom that demands the 9,000–12,000W portable class with a 240V outlet, running near full load for hours. Dual-fuel 10kW+ portables can do it, burning several gallons per hour of charging. If Level 2 backup charging genuinely matters to you (medical needs, essential commute), a standby generator with a transfer switch — installed by a licensed electrician — is the honest recommendation, not a portable.

Why does my EV refuse to charge from the generator?

Usually grounding. Many EVSEs check for a proper ground and see a portable generator’s floating neutral as a fault. Fixes, in order: use an inverter generator with a bonded neutral or add the manufacturer-sanctioned bonding plug; set the charge cord to its lowest amperage; make sure no other loads share the generator (voltage sag mid-session also aborts charging). If the EV maker documents generator charging (some explicitly do), follow their procedure exactly.

Is it cheaper to charge an EV from a generator than to drive a gas car?

No — it inverts the EV’s whole advantage. A portable generator converts a gallon of gas into roughly 2–3kWh delivered to the battery after losses; at a typical 3–4 miles/kWh that is very roughly 8–15 miles per gallon. A modest gas sedan does 2–4× better on the same gallon. Generator charging is an emergency tool, priced accordingly; grid charging is what makes the EV economics work.

Can my EV power my house instead — backwards from this page?

Increasingly, yes, and it is often the better direction to think. Many current EVs offer V2L (vehicle-to-load) outlets supplying 1,800–3,600W — a 60–100kWh battery is the energy equivalent of dozens of generator fuel tanks, silently and indoors-safe. Some (F-150 Lightning, others) support whole-home backup through dedicated equipment installed by an electrician. If you own an EV and worry about outages, investigate its export features before buying a generator at all.

Browse allHome Backup Essentials calculators, combine appliances in themulti-appliance builder, or start from anoutage scenario.

Get the outage prep checklist

Our printable pre-storm checklist — fuel, cords, food-safety windows, safe placement — plus occasional emails when new calculators launch. No spam.

By subscribing you consent to your email being processed by Buttondown to send you these updates — see our privacy policy.