What does kW actually mean when charging an EV?
Kilowatts are speed. Kilowatt-hours are distance. Getting the two straight makes every other charging decision easier.
Two units cause most of the confusion in EV charging, and they are easy to separate with one analogy.
The tap and the bucket
Kilowatts (kW) are the tap. How fast energy flows.
Kilowatt-hours (kWh) are the bucket. How much energy you end up with.
A 7 kW charger running for one hour delivers 7 kWh. A 50 kW charger running for one hour delivers 50 kWh — same time, seven times the energy.
Your battery is measured in kWh because it is a container. Chargers are rated in kW because they are a flow rate.
Turning that into miles
Efficiency is measured in miles per kWh. Most modern EVs manage 3.5 to 4.5 mi/kWh in mixed driving.
So a 7 kW home charger, running for eight hours overnight:
7 kW × 8 hours = 56 kWh
56 kWh × 4 mi/kWh ≈ 224 miles
That is why home charging works so well despite being slow. Overnight is a long time.
Typical rates
| Where | Power | Roughly per hour |
|---|---|---|
| Domestic three-pin | 2.3 kW | ~9 miles |
| Home wallbox | 7.4 kW | ~30 miles |
| Three-phase AC | 22 kW | ~88 miles |
| DC rapid | 50 kW | ~200 miles |
| DC ultra-rapid | 150–350 kW | 600+ miles |
Those DC figures are theoretical maxima that hold only briefly — see why DC charging slows.
The limiting factor
Charging speed is set by the lowest of:
- What the charge point can deliver
- What the car's onboard charger accepts (for AC)
- What the battery will accept right now (for DC — varies with charge level and temperature)
- What the cable is rated for
A 22 kW post charging a car with a 7.4 kW onboard charger delivers 7.4 kW. The post is not faulty; the car is the bottleneck.
This is the single most common source of "my charge was slower than advertised".
Why 22 kW at home usually is not worth it
A 22 kW AC charger needs a three-phase supply. Most UK homes are single-phase, which caps AC charging around 7.4 kW no matter what unit is on the wall.
Upgrading to three-phase is expensive, and for overnight home charging it solves a problem that mostly does not exist — 7.4 kW already refills a typical daily drive several times over while you sleep.
Our charge time calculator shows which of the four limits is binding in any given combination.
In pictures
Common questions
Is a 22 kW home charger three times faster than 7 kW?
Only if your home has a three-phase supply and your car accepts 22 kW AC. Most UK homes are single-phase, which caps AC charging at about 7.4 kW regardless of the unit fitted.
About the author
ElectraMile EditorialEditorial desk
The ElectraMile editorial team covers charging, running costs and EV ownership for readers in the UK and US.
Spotted something wrong? Tell us — we correct and date every change.
Figures shown for United Kingdom in GBP. Switch market in the header to see local pricing and terminology.
