By EV Charge Cost Editorial Team. Published September 28, 2026, updated October 26, 2026.
Power versus energy in one sentence
A kilowatt (kW) is a rate. A kilowatt-hour (kWh) is an amount. Run something that draws 1 kW for one hour and it uses 1 kWh. Run a 7.68 kW charger for 3 hours and it delivers 23.0 kWh.
The water analogy works well: kW is how wide the tap is open, kWh is how many buckets you filled. A wider tap fills the bucket faster, but a bucket of water costs the same either way.
Where each unit shows up
- kW appears on chargers, on the car's charging screen and in spec sheets for the onboard charger and DC fast charging. It tells you speed.
- kWh appears on your electricity bill, on public charging receipts, in battery capacity figures and in the EPA efficiency rating (kWh per 100 miles). It tells you quantity, and quantity is what you pay for.
A typical EV in our data uses 33.5 kWh per 100 miles. That figure is measured at the wall, so it already includes charging losses. Multiply it by your price per kWh and you have your cost per 100 miles: $6.08 at the U.S. average price.
The two formulas you actually need
- Charging time (hours) = kWh needed ÷ charger kW.
- Charging cost = kWh needed × price per kWh.
Notice that kW appears only in the time formula. A faster home charger shortens the session but does not change the cost of the energy. In our example, 3 hours on a 7.68 kW charger adds 23.0 kWh, about 69 miles for the typical EV, and costs $4.18 at 18.16¢/kWh.
What an overnight session delivers at each power level
The table shows how much energy a 8-hour overnight session delivers at common home charging power levels, and what that energy costs at the U.S. average residential price.
| Charger | Power (kW) | kWh in 8 h | Miles added | Cost of that energy |
|---|---|---|---|---|
| Level 1 — 120 V, 12 A | 1.44 | 11.5 | 34 | $2.09 |
| Level 2 — 240 V, 16 A | 3.84 | 30.7 | 92 | $5.58 |
| Level 2 — 240 V, 32 A | 7.68 | 61.4 | 183 | $11.16 |
| Level 2 — 240 V, 40 A | 9.60 | 76.8 | 229 | $13.95 |
| Level 2 — 240 V, 48 A | 11.52 | 92.2 | 275 | $16.74 |
The cost column grows only because more kWh flow in the same number of hours. If you need a fixed amount of energy, say 30 kWh, it costs $5.45 at 18.16¢/kWh on any of these chargers. The faster one just finishes sooner.
When kW can affect what you pay
There are a few cases where power level indirectly matters for cost:
- Time-of-use windows. If your cheap overnight window is short, a low-kW charger may not finish inside it, and the rest of the energy is bought at a higher rate. See time-of-use rates and EV charging.
- Per-minute public pricing. Some public chargers bill by time rather than by energy. Then a car that accepts more kW gets more kWh per paid minute, and a slow-charging car pays more per kWh.
- Charging losses. Very low-power charging spends a larger share of the session powering the car's electronics, so a bit more of each kWh is lost. The difference is modest; see where charging losses come from.
Common mix-ups
- "My charger is 11 kWh." It is 11 kW. A charger has a power rating; a battery or a bill has an energy amount.
- "A bigger battery costs more per mile." Not by itself. Cost per mile follows kWh per mile, not battery size.
- "Fast charging uses more electricity." It uses a similar amount of energy per mile; public fast charging usually just costs more per kWh. At an example price of $0.45/kWh, the typical EV would cost $15.08 per 100 miles versus $6.08 at home.
To see how long any charge takes at a given kW, use the charging time calculator. To turn kWh into dollars at your own rate, use the charging cost calculator.