By EV Charge Cost Editorial Team. Published September 28, 2026, updated October 26, 2026.
Why there are two numbers
Automakers do not let you use every kWh in the pack. The battery management system keeps a buffer at the top and bottom of the charge window because lithium-ion cells age faster when held at very high or very low states of charge. Some cars also reserve a small margin so the dashboard can show 0% while a little energy remains.
The result: a car may be advertised with one battery size (often the gross figure), while the car can only draw a smaller usable amount. Take an illustrative pack of 80 kWh gross and 75 kWh usable. The 5 kWh difference is never charged or discharged in normal use, so you never pay for it.
What your bill actually pays for
When you charge from a low state to full, you pay for the usable kWh that go into the battery plus the energy lost on the way. Using the illustration, filling 75 usable kWh with an illustrative 10% charging loss takes about 83.3 kWh from the wall. At the U.S. average price of 18.16¢/kWh, that is $15.13; at Nevada's 12.72¢/kWh it is $10.60, and at Hawaii's 47.18¢/kWh it is $39.32.
So if you estimate a full charge with the gross figure you overstate the energy stored, and if you use the usable figure alone you understate the energy bought. Neither is quite right on its own.
A shortcut that skips battery size entirely
You do not need to know either capacity to estimate cost. The EPA rating in kWh per 100 miles is measured at the wall, so it already reflects usable energy and charging losses. Multiply the EPA range by the rating and you get the wall energy for a full-range charge, the number that matters for your bill.
| Model | kWh/100 mi | EPA range (mi) | Wall kWh for full range | At 18.16¢ | Nevada | Hawaii |
|---|---|---|---|---|---|---|
| Tesla Model 3 | 26.4 | 346 | 91.3 | $16.57 | $11.61 | $43.08 |
| Tesla Model Y | 26.9 | 337 | 90.5 | $16.44 | $11.51 | $42.70 |
| Chevrolet Equinox EV | 32.6 | 307 | 100.1 | $18.18 | $12.73 | $47.23 |
| Hyundai Ioniq 5 | 34.5 | 269 | 92.8 | $16.85 | $11.80 | $43.78 |
| Ford F-150 Lightning | 47.9 | 320 | 153.3 | $27.84 | $19.50 | $72.33 |
| Kia EV9 | 40.0 | 283 | 113.2 | $20.56 | $14.40 | $53.41 |
Figures use each model's representative trim. The wall-energy column is larger than the car's usable battery, because it includes the energy lost while charging. It is not a battery size.
Where the difference matters in practice
Comparing cars
Two cars with the same advertised battery can have different usable capacities and very different efficiency. For running cost, compare kWh per 100 miles, not pack size. The vehicle pages list the rating for every current model.
Reading a public charging receipt
A DC fast charger meters energy at the station. It will not match the car's percentage gain exactly, because of losses in the cable and battery and because the percentage is based on usable capacity. A receipt showing a few kWh more than you expected is normal.
Watching the buffer over time
As a battery ages, some cars quietly shrink or release the buffer, so the usable figure can shift. This changes range more than cost per mile; see battery degradation and charging cost.
Using a battery percentage to estimate a session
If you know usable capacity, the energy added in a session is roughly the percentage gained times usable kWh. With the 75 kWh illustration, going from 30% to 80% stores 37.5 kWh in the battery. Divide by (1 − loss share) to get what the meter records: about 41.7 kWh at an illustrative 10% loss, or $7.57 at 18.16¢/kWh. Using gross capacity here would overstate the energy by the size of the buffer.
How to estimate your own full-charge cost
- Find your car's EPA kWh per 100 miles and range on its vehicle page.
- Multiply range by kWh per 100 miles and divide by 100 to get wall kWh.
- Multiply by your price per kWh. Or skip the math with the full-charge cost guide.