EV Range and Charging Basics: kW, kWh, Charging Levels and Cold Weather

Two units explain almost everything about living with an electric car. A kilowatt-hour (kWh) is an amount of energy: how much the battery holds. A kilowatt (kW) is a rate: how fast energy goes in or out. Battery size in kWh is the tank. Charger power in kW is the pump. Once that is clear, the rest of the numbers on a spec sheet fall into place.

The three numbers on the label

The EPA label on a new EV's window sticker gives you three figures worth understanding.

Number	What it tells you	How to use it
Driving range (miles)	Approximate miles on a full charge in combined city and highway driving	Compare cars; plan with a margin
kWh per 100 miles	How much electricity the car uses	Work out your cost per mile. Lower is better.
MPGe	Miles on the amount of electricity with the same energy as a gallon of gasoline	Rough comparison with gas cars; less useful for costs

Working out cost per mile

Multiply kWh per 100 miles by your electricity price, then divide by 100.

The Department of Energy's example: a car that uses 27 kWh per 100 miles, charged at 10.7 cents per kWh, costs about 3 cents per mile. Your rate is on your electric bill and may be quite different. Run the same sum with the per-kWh price at a public fast charger near you, and you will see why where you charge matters so much.

A small amount of energy is lost during charging, so the electricity you pay for is a bit more than what reaches the battery. fueleconomy.gov notes charging efficiency is often between 84 and 93 percent.

EPA range vs the range you will get

EPA range comes from standardized tests so that cars can be compared fairly. The label itself says actual results will vary. The main things that change it:

Speed. Air resistance rises quickly with speed. Unlike gas cars, EVs are usually more efficient in town than on the highway, so sustained fast highway driving often returns less than the rated range.
Temperature. Cold and, to a lesser degree, heat. See the section below.
Climate control. Heating draws from the drive battery.
Terrain and load. Climbing, towing, roof boxes and a full car all cost range. Towing in particular can reduce it dramatically.
Tires and wheels. Larger wheels and winter tires often reduce efficiency. The same model can carry different range ratings depending on wheel size, so check the rating for the exact trim.
Battery age. Capacity declines slowly over time. See used EV battery health.

A practical habit: treat the rated range as a best-normal-day figure, and plan regular trips so they use well under it. Also note that most owners do not use 100 to 0 percent day to day. Manufacturers often recommend a daily charge limit below full for some battery types, and no one likes arriving near empty, so your usable everyday range is a slice of the total.

Charging levels

These figures are from the Department of Energy's Alternative Fuels Data Center.

Level	Power source	Typical speed	Where you find it	Best for
Level 1	120-volt household outlet	About 5 miles of range per hour	Home, with the cord that comes with many cars	Short daily mileage, overnight
Level 2	240 volts at home, 208 volts commercial	About 25 miles of range per hour	Home wall units, workplaces, shopping centers, hotels	Daily charging for most drivers
DC fast charging	High-power direct current	About 100 to 200 or more miles of range in 30 minutes	Highway corridors, dedicated charging sites	Road trips, quick top-ups

Some details behind the table:

Level 1 needs no installation if you have an outlet on a suitable circuit near where you park. Eight hours overnight adds around 40 miles for a mid-size EV.
Level 2 equipment ranges from 2.9 to 19.2 kW. Most home units deliver about 7.2 kW and need a dedicated 40-amp circuit, installed to local code and often with a permit. Your car's onboard charger sets the ceiling: a car that accepts 7 kW will not charge faster on an 11 kW unit.
DC fast charging bypasses the onboard charger and feeds the battery directly. Stations are rated up to several hundred kW, but the car decides how much it takes.

Connector types (J1772, CCS, J3400 or NACS, and CHAdeMO) determine which stations a car can use. That is covered in the first-time EV buying guide.

A quick way to estimate charging time

Divide the energy you need (kWh) by the power (kW) to get hours.

Example with round numbers: adding 40 kWh on a 7 kW home charger takes about 40 ÷ 7, a little under 6 hours. That simple division works well for Level 1 and Level 2. It does not work for fast charging, because of the charging curve.

The charging curve

A fast charger does not deliver its peak power the whole time. The car controls the rate to protect the battery, and the pattern is called the charging curve. In general:

Power is highest when the battery is at a low state of charge and warm.
It tapers as the battery fills, and slows markedly somewhere past about 80 percent.
A cold battery charges more slowly. Many cars can warm the battery on the way to a charger if you set the charger as your navigation destination.

This is why EV road trips work differently from gas ones:

Plan around 10 to 80 percent. The last 20 percent can take as long as the first 60 or 70. It is usually quicker overall to stop a little more often and leave at around 80.
Compare cars on charging time, not peak kW. A car that holds a moderate rate for a long time can beat one with a higher peak that drops off quickly. The useful spec is minutes from 10 to 80 percent, and how many miles that adds.
A bigger station number is not always faster for you. A 350 kW station cannot push more than your car accepts. A car limited to 150 kW charges at up to 150 kW there.

When you compare two EVs, ask for or look up: peak DC charging power, the 10 to 80 percent time, and the Level 2 onboard charger rating in kW.

Cold weather

Cold affects all vehicles, and EVs more visibly. fueleconomy.gov, citing a 2019 AAA study, reports that at 20°F compared with 75°F:

With the cabin heater on, EV range fell about 41 percent in mixed city and highway driving.
About two-thirds of the extra energy went to heating the cabin.
With the heater off, range was about 12 percent lower.

Models differ, and newer cars with heat pumps tend to lose less to cabin heating, but plan on a real reduction in winter. Things that help, from fueleconomy.gov and common practice:

Preheat the cabin while the car is still plugged in, so the energy comes from the wall.
Use seat and steering wheel heaters, which use less energy than heating all the air in the cabin.
Park in a garage when you can.
Keep tires at the recommended pressure, which drops in cold weather.
Expect slower fast charging on a cold battery and use battery preconditioning if the car has it.

Putting it together when you shop

For each EV you are considering, write down:

EPA range for the exact trim and wheel size
kWh per 100 miles, and your cost per mile at home and at a nearby fast charger
Onboard charger rating (kW) for Level 2
Peak DC fast charging power and the 10 to 80 percent time
Whether it has a heat pump and battery preconditioning
Charge port type and adapter availability

Then check the range against your longest regular day with a winter margin. You can look up and compare official range and efficiency figures for any model on fueleconomy.gov, and see what the cars are actually listed for on /cars. If you are still weighing a plug against no plug, hybrid vs plug-in hybrid vs EV lays out the trade-offs, and total cost of ownership helps you put a number on them.

The short version