Electric car charging speed guide: kW, kWh and what they mean at the plug

kW vs kWh: what is the difference?

These two units are frequently confused, but they describe different things.

kW (kilowatt): charging speed

kW is the rate at which energy is delivered. Think of it as the width of the pipe supplying water to a tank: a wider pipe fills the tank faster. A 7 kW charger delivers energy twice as quickly as a 3.5 kW charger. Higher kW always means a shorter charging time for the same battery.

kWh (kilowatt-hour): battery capacity

kWh is the total amount of energy the battery can store, equivalent to the size of the tank. A larger kWh figure means more range, but also a longer charging time on the same charger. A 100 kWh battery takes roughly twice as long to charge as a 50 kWh battery at the same kW rate.

The charging time formula: battery capacity (kWh) divided by charger power (kW), multiplied by about 1.1 to account for charging losses, gives you the approximate hours. A 75 kWh battery on a 7 kW charger: 75 ÷ 7 × 1.1 = approximately 11.8 hours.

The four EV charging speed tiers in the UK

All UK charge points fall into one of four speed tiers. Each tier suits a different use case.

Slow AC (3 to 7 kW)

Found on lamp post chargers, on-street units, and standard 3-pin sockets. Adds approximately 15 to 25 miles per hour. Suited to overnight top-ups for low daily mileage or extended parking at a destination. Impractical as a sole charging method for most drivers.

Fast AC (7 to 22 kW)

The standard for home wallboxes and the most common public charge point type at supermarkets, leisure centres, and hotels. A 7 kW home wallbox adds approximately 25 to 40 miles per hour and charges most EVs overnight. Fast AC chargers at 22 kW are available at some commercial sites but require a three-phase electricity supply, which most domestic properties do not have.

Rapid DC (50 to 150 kW)

Found at motorway services, fuel station forecourts, and dedicated charge hubs. Adds approximately 100 to 200 miles in 20 to 40 minutes. This is the charger you use during a long-distance motorway journey to top up before continuing.

Ultra-rapid DC (150 to 350 kW)

Growing rapidly across UK motorway corridors: 40% more ultra-rapid points in January 2026 versus January 2025. Can add 10 to 80% in 15 to 25 minutes for vehicles with 800V battery architecture. For 400V vehicles, the charger works but delivers only up to the car's maximum DC acceptance rate.

AC vs DC charging: why the distinction matters

Understanding the difference between AC and DC charging explains a common source of confusion: why a car does not always charge at the charger's rated speed.

AC charging and the onboard charger

AC (alternating current) is the type of electricity supplied to your home and to most public charge points. Your EV has a built-in onboard charger that converts AC to DC (direct current) before storing it in the battery. The onboard charger has a maximum rated power: typically 7.4 kW or 11 kW on most UK models, though some cars accept up to 22 kW AC.

This is the critical point: the onboard charger rate sets the ceiling for AC charging speed, not the charger you connect to. If your car's onboard charger is rated at 7.4 kW and you connect to a 22 kW public AC charger, your car will charge at 7.4 kW. The charger's extra capacity is simply unused.

DC charging: bypassing the onboard charger

DC rapid charging delivers power that is already converted to direct current, bypassing the onboard charger entirely and going straight to the battery. The car's maximum DC acceptance rate, specified in its technical documentation, sets the ceiling. This is why rapid chargers can be so much faster: they are not constrained by the onboard charger's relatively modest rating.

To find your car's maximum DC acceptance rate, check the manufacturer's spec sheet under "maximum DC charging power" or equivalent. This figure tells you the fastest you can ever charge at a rapid charger, regardless of how powerful the charger itself is.

Connector types in the UK

• Type 2 (Mennekes): The standard AC connector for home wallboxes and public AC charge points across the UK and Europe. All modern EVs sold in the UK include a Type 2 socket.
• CCS (Combined Charging System): The standard DC rapid charging connector for the vast majority of modern EVs in the UK. CCS2 combines the Type 2 AC inlet with two additional DC pins below.
• CHAdeMO: An older DC standard used by some earlier Nissan Leaf, Nissan e-NV200, and Mitsubishi models. CHAdeMO infrastructure is declining and fewer new chargers are being installed with this connector.

How charging speed affects your home charger choice

For most UK homes with a single-phase electricity supply, a 7 kW home wallbox is the right choice. It matches the onboard AC charger rate of the majority of EVs sold in the UK and fully charges most models overnight.

If your car has an 11 kW onboard charger, some home wallboxes support three-phase 11 kW charging if your property has a three-phase supply. This can reduce overnight charge time from roughly 11 hours to approximately 8 hours for a 75 kWh battery, though the saving in a domestic context is modest.

Smart chargers add features relevant to BestChargers' readers: solar diversion (charging only when your panels are generating surplus energy), off-peak scheduling, load balancing, and app monitoring. See our home EV charger reviews for a full comparison of the leading models.

What charging speed does your car actually accept?

Three steps to find the numbers that matter for your car:

1. Look up the car's specification on the manufacturer's UK website.
2. Note the "onboard AC charger" rating: this is your maximum AC charging speed in kW.
3. Note the "maximum DC charging power": this is your maximum rapid charge speed in kW.

These two figures tell you the fastest any charger can ever charge your specific car. No charger, however powerful, can exceed them.