A kilowatt (kW) is power. A kilowatt-hour (kWh) is energy. Power is the rate. Energy is the amount. One kilowatt running for one hour delivers one kilowatt-hour. That is the whole distinction. Everything else on an EV spec sheet is that pair attached to different parts of the car.
Utility pages already teach the lamp-and-bill version. This page attaches the same units to a live catalog: battery kWh, motor kW, DC peak kW, and Wh/km. Snapshot 5 September 2026. 1,372 available rows in the evstats.org file.
Table of Contents
- kW is a rate, kWh is a quantity
- The formula, and when it stops working
- Four numbers on one EV spec sheet
- Charging: kW on the stall, kWh on the receipt
- Efficiency is neither kW nor a second kWh
- Mix-ups that keep showing up
- Quick answers
- Sources
kW is a rate, kWh is a quantity
The SI unit of power is the watt. NIST’s SI guide writes it as W = J/s: one joule of energy per second. A kilowatt is one thousand watts (NIST SP 811, Table 5, updated 18 August 2025).
The EIA glossary calls a kilowatt-hour the energy of 1 kW expended for 1 hour. NIST’s conversion tables set 1 kWh = 3.6 MJ = 3,600,000 J exactly (SP 811 Appendix B.8). That is not a rule of thumb. It is 1,000 W × 3,600 s.
A speedometer is kW. An odometer is kWh. The tap is kW. The bucket is kWh. Those analogies are table stakes. They still help, because the letters look alike and the mistake is cheap.
EIA’s own classroom example: a 40 W lamp (0.04 kW) left on for 5 hours uses 0.2 kWh. Same arithmetic as a 7 kW wallbox left on for 2 hours: 14 kWh into the pack, before losses.
The formula, and when it stops working
Energy (kWh) = power (kW) × time (hours) only when power is constant. A kettle is close enough. A DC stall is not.
A 2025 DOE/NREL station study describes the usual curve: the battery accepts high power at low state of charge, then tapers as it fills and as temperature leaves the window. Session energy is the area under that curve, not nameplate kW times the minutes you stood there.
So a back-of-envelope 10–80% time of “50 kWh ÷ 150 kW = 20 minutes” is a ceiling check, not a timetable. The charging simulator exists because the curve is the job. The fastest-charging leaderboard lists peak kW, which is the other number.
Four numbers on one EV spec sheet
One car carries at least four different measurements that people collapse into “how big is it.”
| Field | Unit | What it is |
|---|---|---|
| Battery | kWh | Energy stored (catalog figure; usable vs gross is not split in this file) |
| Motor / system output | kW | Peak mechanical power |
| DC peak | kW | Highest charge rate the car will ask for |
| Efficiency | Wh/km | Energy per distance on the WLTP cycle |
Available rows in this catalog on 5 September 2026:
| Row | Battery | Motor | DC peak | Efficiency |
|---|---|---|---|---|
| Catalog average (n=1,372) | 71.5 kWh | 234 kW | 168 kW | 187 Wh/km |
| Dacia Spring Electric 45 | 25 kWh | 33 kW | 34 kW | 152 Wh/km |
| Lucid Air Grand Touring (MY25–26) | 117 kWh | 611 kW | 300 kW | 163 Wh/km |
The Spring’s motor and its DC peak sit in the same 30 kW band. The Lucid’s motor (611 kW) and DC peak (300 kW) are different jobs. Mixing them is how a buyer reads “300 kW” as “this car is twice as powerful as a 150 kW car” when the 300 is a charge ceiling.
Those rows are in the catalog. Put two of them side by side in the comparison tool if you want the rest of the sheet.
Charging: kW on the stall, kWh on the receipt
NIST Handbook 130 (2026) is blunt about retail EV fuel: energy sold at the plug is in kilowatt-hours, not minutes. The same handbook calls the charger’s stated capability nominal power, in kilowatts: the rate of transfer, not the quantity transferred.
That is why a “150 kW stall” and a “40 kWh session” can both be true. One is the ceiling. The other is what the meter billed. Home AC is the same split: an 11 kW wallbox is the rate; overnight you might add 40 kWh.
The car’s onboard AC charger is a third kW number. A 22 kW post does not help if the car’s AC inlet is 7.4 kW. DC bypasses that box. Peak DC is still a ceiling, not a promise. EV charging levels is the Level 1 / 2 / DC map. Charging cost is the bill in currency, which is kWh times a tariff.
Efficiency is neither kW nor a second kWh
Wh/km (or kWh/100 km, or kWh/100 mi on a US label) is energy per distance. It is not power. It is not pack size. EPA’s EV label uses kWh/100 mi and includes charging losses, so wall energy is larger than pack energy (EPA, fuel-economy EV testing, updated 1 July 2026). The same sticker prints MPGe.
Catalog average efficiency here is 187 Wh/km, which is 18.7 kWh/100 km on the WLTP cycle. That is a laboratory distance number. Winter highway is a different experiment. The TCO calculator turns kWh into money over years. It still needs you to know which number you typed.
Mix-ups that keep showing up
Writing kW/h. A kilowatt already has time in the denominator (joules per second). “Kilowatts per hour” is not how grids or cars are billed. The unit is kWh: kilowatt times hour.
Calling a charger “75 kWh.” Some product pages print kWh on a power rating. That is a label error, not a third unit. The stall is kW. The session is kWh.
Reading battery kWh as horsepower. 80 kWh is the tank. 239 kW is how hard the motors can push. They do not convert 1:1.
Assuming catalog kWh is usable. This file stores one battery number per row. Manufacturers publish usable, gross, or a rounded brochure figure. We do not split them. Treat the cell as “the number we have,” not as EPA usable battery energy. The catalog mean, median, and size bands are on average EV battery capacity.
Broader spec hygiene sits in EV specifications.
Quick answers
What is the difference between kW and kWh? kW is how fast energy moves. kWh is how much has moved. One kW for one hour is one kWh.
How do you convert kW to kWh? Multiply constant power by hours. 11 kW × 4 h = 44 kWh. Skip the shortcut when the DC curve is moving.
Why does the bill show kWh? The meter sells energy. EIA’s unit for that energy is the kilowatt-hour.
Does a 350 kW stall charge every car at 350 kW? No. The car’s DC peak, temperature, and fill level decide. Catalog average DC peak is 168 kW.
Which number do I use to compare cars? Pack kWh for how far the tank can go. Motor kW for how hard it accelerates. DC kW for how fast a stall can refill it. Wh/km for how hungry it is. Open the catalog if you want all four on one row.
Sources
- NIST SP 811, SI units and conversion factors (watt = J/s; 1 kWh = 3.6 MJ). https://www.nist.gov/pml/special-publication-811
- EIA, Measuring electricity; EIA glossary (kW rate, kWh = 1 kW for 1 hour). https://www.eia.gov/energyexplained/electricity/measuring-electricity.php
- NIST Handbook 130 §2.33 (2026): EV fuel sold in kWh; nominal power in kW.
- DOE/NREL, Station Impact Analysis 2025 (DC power is not constant).
- EPA, Fuel economy and EV range testing (kWh/100 mi includes charging losses), 1 July 2026.
- evstats.org catalog extract, 5 September 2026, 1,372 available rows.