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Start with the unit on your screen
A kilowatt-hour (kWh) measures energy. Miles per kWh (mi/kWh) expresses distance for that energy; kWh per mile expresses energy for a distance. The US fuel-economy label uses kWh per 100 miles. FuelEconomy.gov explains the label’s consumption units.
- Calculate miles/kWh: miles driven ÷ kWh used over the same trip and on the same energy-measurement basis.
- Estimate trip energy: miles to drive ÷ expected miles/kWh.
- Convert energy to distance: kWh × expected miles/kWh.
For example, a hypothetical 120-mile trip using 40 kWh works out to 3 miles/kWh. On that same basis, 20 kWh at 3 miles/kWh corresponds to 60 miles. Neither calculation establishes how much usable energy is currently in your battery.
kW is a power rating, not an energy quantity or an efficiency figure. The connectors and power guide explains what to check on a charger listing.
Convert miles/kWh, Wh/mile and kWh/100 miles
There is no fixed number of kWh in one mile: you need an efficiency assumption. Use 1 ÷ miles/kWh for kWh/mile, or 100 ÷ miles/kWh for kWh/100 miles. These are unit conversions, using the energy-consumption definition on the EPA label; they are not vehicle test results.
| Miles/kWh | kWh/mile | Wh/mile | kWh/100 miles |
|---|---|---|---|
| 2 | 0.5 | 500 | 50 |
| 2.5 | 0.4 | 400 | 40 |
| 3 | 0.333 | 333.3 | 33.3 |
| 4 | 0.25 | 250 | 25 |
| 5 | 0.2 | 200 | 20 |
If your screen shows Wh/mile, divide by 1,000 to get kWh/mile. To get miles/kWh instead, divide 1,000 by Wh/mile. For example, 250 Wh/mile = 0.25 kWh/mile = 4 miles/kWh. Higher miles/kWh means less energy per mile; lower Wh/mile or kWh/100 miles means less energy per mile.
For kWh/100 km, use 100 ÷ (miles/kWh × 1.609344). Thus 4 miles/kWh is about 15.5 kWh/100 km. This uses NIST’s international-mile conversion of 1 mile = 1.609344 km. Changing distance units does not change which energy is being measured.
Is 2.5, 3 or 5 miles/kWh good?
On the same measurement basis, 5 miles/kWh uses less energy for a given distance than 3 or 2.5. But a single reading cannot tell you whether a car is performing well for its conditions. The EPA identifies cold weather, accessory use and high-speed driving as factors affecting range.
For a useful comparison, check the same vehicle, a comparable journey and the same display period. A short recent-trip reading and an average across months answer different questions. Treat an unusually favorable reading as an observation, not a promise for the next leg.
Your manual can help explain what changed. The 2026 Mustang Mach-E US manual describes a trip-energy breakdown covering climate, driving and route, accessories, and outside temperature. That is one model’s display, not a definition of every EV’s dashboard.
A reading of 3.2 miles/kWh converts to about 31.3 kWh/100 miles; 5 converts to 20. Use those conversions to understand a reading, not to award a universal “good” score. For standardized vehicle comparisons, use the EPA label and keep its charging-loss accounting in mind.
Estimate what you need to add at the stop
Hypothetical example: 120 miles ahead, an assumed battery-side efficiency of 3 miles/kWh, 18 kWh currently usable in the battery, and a chosen 8 kWh arrival reserve. These are teaching assumptions, not measurements from a vehicle or a recommended reserve.
| Step | Calculation | Result |
|---|---|---|
| Energy for the drive | 120 miles ÷ 3 miles/kWh | 40 kWh |
| Include the assumed arrival reserve | 40 + 8 | 48 kWh |
| Subtract energy already usable | 48 − 18 | 30 kWh to add to the battery |
The general budget is trip energy + chosen arrival reserve − energy already usable. If the result is negative, the arithmetic budget calls for zero additional energy. That result alone does not validate a route or a charging plan.
Now change only the efficiency assumption to 2.5 miles/kWh. The drive needs 48 kWh, and the same budget becomes 48 + 8 − 18 = 38 kWh to add. This 8 kWh difference shows why the efficiency assumption matters; it is not a forecast of weather or driving conditions.
If you do not know the usable energy remaining, leave that input unknown. Do not treat a battery-percentage display multiplied by a quoted pack size as an exact measurement. Use your vehicle’s current trip-planning guidance and arrival-charge estimate, follow its charging limits, and allow for a backup stop.
The EPA describes range estimates as comparison guidance and explains why actual range varies. This worksheet helps interpret an estimate; it cannot guarantee arrival.
Keep battery energy separate from billed energy
Before comparing two numbers, ask where each came from: the trip screen, the EPA label or the charging receipt. FuelEconomy.gov explicitly states that plug-in MPGe and kWh/100-mile estimates include charging losses. Converting an EPA figure to miles/kWh preserves that accounting; it does not turn it into a battery-only figure.
Do not add a generic charging-loss allowance to an EPA estimate that already includes those losses. Likewise, do not assume your dashboard’s energy figure and a public charger’s billed kWh measure exactly the same thing. Check the vehicle’s definition and the session receipt.
The worked example’s 30 kWh is an assumed addition to stored battery energy, not a promised receipt quantity. Separately, a hypothetical receipt showing 20 kWh billed at $0.40/kWh has an $8 energy charge. That calculation says nothing about parking, session fees or other charges.
Use the public EV charging cost guide to compare the whole bill. Driving efficiency in miles/kWh and charging efficiency, meaning how much supplied energy reaches storage, are different questions.
Use the estimate to choose a practical stop
- Use your vehicle’s trip planner to check the next leg and expected arrival charge. Revisit the estimate if the trip conditions change.
- Compare charging options in the US charging directory. Check the actual connection, access hours and restrictions for the stop you intend to use.
- Match the likely charging break to your plans. The charging-time guide explains why a charger’s maximum kW does not establish the length of your session.
DOE’s charging-equipment guidance lists starting battery charge, capacity, vehicle equipment and charger type among the factors affecting duration. Miles/kWh helps with the energy side of that decision; it does not settle compatibility, charging speed or whether a port is free when you arrive.
Sources and check dates
This is source-researched guidance, not an on-site inspection. Check the operator’s current terms for your visit. The dates below record when each source was checked; they do not establish when the source’s information was last verified.
- FuelEconomy.gov: understanding the electric vehicle label — checked
- FuelEconomy.gov: fuel-economy data and charging losses — checked
- EPA: electric vehicles and factors affecting range — checked ; source date: 2026-08-06
- Ford: 2026 Mustang Mach-E US owner's manual, Trip Data — checked
- NIST: revised unit conversion factors — checked ; source date: 2026-02-03
- DOE Alternative Fuels Data Center: charging equipment and charging time — checked