You bought your first electric car. The salesperson said it has a "75 kWh battery." Your home wallbox is rated "7.4 kW." A public DC fast charger advertises "150 kW peak." You plug in, expecting a smooth math story — and within a week, you have three confused questions, a slightly higher-than-expected bill, and one mystifying app that switched from "minutes" to "kWh" mid-session.
Welcome to the most common unit-conversion stumble of the EV era. kW and kWh are not the same thing — they differ by exactly the same conceptual gap as miles per hour differs from miles. Once that clicks, every charging spec sheet, every utility bill, and every public-charger receipt suddenly makes sense.
The one-line difference
- kW (kilowatt) — a rate. How fast energy is moving in or out, right now.
- kWh (kilowatt-hour) — an amount. The total energy that has flowed.
Drive at 60 mph for one hour and you cover 60 miles. Charge at 7 kW for one hour and you add 7 kWh. The math is the same: `rate × time = amount`. The unit just changes from miles to kWh.
That's the whole framework. Everything below is consequences.
How big is your battery, really?
Modern EV battery specs are quoted in kWh:
| Vehicle class | Typical battery |
|---|---|
| Compact (Nissan Leaf, Renault Zoe) | 40–62 kWh |
| Mid-size (Tesla Model 3, Hyundai Ioniq 5) | 60–82 kWh |
| Large SUV (Tesla Model X, Rivian R1S) | 100–135 kWh |
| Luxury / long-range (Lucid Air) | 112–118 kWh |
Range is roughly battery (kWh) ÷ consumption (kWh per 100 km or per 100 mi). A 75 kWh Model 3 averaging 16 kWh/100 km gets about 470 km real-world range. The math is honest; manufacturer claims usually aren't.
Charging speed: the kW you'll actually see
Charger ratings are quoted in kW. Translating to "range added per hour" requires multiplying by your car's efficiency. As a rule of thumb:
- 1 kW of charging ≈ 5–6 km of added range per hour for an efficient sedan
- 1 kW ≈ 3–4 km/h for a heavy SUV or pickup
So a 7 kW home wallbox adds about 35–45 km of range per hour. A 22 kW destination charger adds 110–130 km/h. A 150 kW DC fast charger — at peak — adds 750–900 km of range per hour, but as you'll see in a moment, peak is not the whole story.
Level 1, Level 2, DC fast — the three speed tiers
Level 1 (1.4–2.4 kW) — a regular household outlet. Worst-case for impatience: you'll add roughly 8–13 km of range per hour. Fine for plug-in hybrids and overnight trickle-charges, painful for full EVs unless you drive less than 50 km a day.
Level 2 (3.7–22 kW) — the dedicated wallbox at home, or a destination charger at a hotel or shopping mall. The 7.4 kW (single-phase, 32 A) and 11 kW (three-phase, 16 A) ratings cover most of Europe and North America. A full 0–100% charge of a 75 kWh battery takes roughly 10 hours at 7.4 kW or 7 hours at 11 kW.
DC fast charging (50–350 kW) — highway corridor charging. Skips the car's onboard AC-to-DC converter entirely and pushes DC directly into the battery. Modern 800-volt platforms (Hyundai E-GMP, Porsche Taycan, Lucid) accept the full advertised speed; older 400-volt cars often cap around 100–150 kW even on a 350 kW post.
The peak-vs-average gotcha
This is where the math really starts hiding things. When a charger advertises 350 kW, that's its peak output. The car can only accept that peak inside a narrow battery state-of-charge window — typically 10% to 40%. Above 60–70% the car automatically tapers to protect the battery's chemistry. By 80%, you might be down to 60 kW; by 95%, often under 30 kW.
Real average over a 10–80% session is usually 100–150 kW even on a 350 kW post. Plan stops to arrive low (10–20%) and leave at 70–80%, not 100% — the last 20% takes nearly as long as the first 60%.
Reading your electricity bill: the dollar/euro side
Utilities bill in kWh, not kW. A typical residential rate is €0.20–0.40 per kWh in Europe, $0.10–0.30 in North America (with wide regional variation, and time-of-use tariffs that can swing the price by 4× between off-peak and peak).
Cost of a "fill-up" at home: a 75 kWh battery from 10% to 80% is 70% × 75 = 52.5 kWh. At €0.30/kWh that's €15.75 — typically equivalent to about 600 km of driving. Compare to a petrol car burning 7 L/100 km at €1.70/L: €71 for the same distance.
Public DC fast chargers, on the other hand, often charge €0.50–0.79/kWh — roughly the same per-km cost as petrol. Home charging is the killer-app economy of EV ownership; road-trip charging is convenience tax.
The minute-billing trap
Some public chargers — especially older Tesla Superchargers in idle-fee mode, and a handful of European networks — bill per minute rather than per kWh. The intent is fair: a slow car shouldn't tie up a 350 kW post and pay only for what it absorbs.
The unintended effect: if you arrive at 80% (with charging already tapered), you might be paying €0.50/min while only pulling 40 kW — that's effectively €0.75/kWh. Always check the pricing model before plugging in. The same kWh can cost wildly different amounts depending on the math the operator chose.
Quick reference: what each kW number actually means
| Charger | Power | Realistic range/hour | Time for 50 kWh |
|---|---|---|---|
| Standard outlet (Level 1) | 1.8 kW | ~10 km/h | ~28 hours |
| Home wallbox single-phase | 7.4 kW | ~40 km/h | ~7 hours |
| Home wallbox three-phase | 11 kW | ~60 km/h | ~4.5 hours |
| Destination charger | 22 kW | ~120 km/h | ~2.3 hours |
| Highway DC (older) | 50 kW | ~270 km/h peak | ~1 hour to 80% |
| Highway DC (modern) | 150 kW | ~800 km/h peak | ~25 min to 80% |
| Highway DC (800-V class) | 350 kW | ~1900 km/h peak | ~18 min to 80% |
The five-second framework to keep straight
Whenever a charging spec confuses you, ask yourself which question it's answering:
Mix up #1 with #2 and you'll think your home wallbox can charge your car in an hour. Mix up #3 with #4 and you'll be surprised by your road-trip bill. Get them right and the EV math story falls into place — battery, charger, time, energy, money — all from the same simple `rate × time = amount` rule that took you ten minutes to learn for high-school physics.
The good news: every spec sheet, every app, every utility bill is now decipherable. The better news: this same framework applies to solar panels (kW = panel rating, kWh = energy generated), home batteries, and even your microwave oven. Once you can see the difference between a rate and an amount, you stop being surprised by units forever.