EV Charger Cable Size: Rules of Thumb and Sizing Table

If you are searching for an "EV charger cable size calculator", the honest answer is that no web box can safely size the fixed supply wiring for your home. The typical conductor for a 7kW (32A) home charger is often 6mm² for ordinary run lengths and 10mm² for longer runs, but the exact size depends on your run length, installation method, grouping, ambient temperature and voltage drop, and it must be confirmed by a qualified electrician to BS 7671. For a quick orientation, use the reference table below, then read our pillar guide on what size cable for an EV charger and book an installer.

What does "cable size" actually mean here?

The word "cable" is doing two very different jobs, and most calculators confuse them. Getting this straight saves you a lot of wasted searching.

The supply cable (fixed wiring, measured in mm²)

This is the fixed wiring an electrician runs from your consumer unit (fuse box) to the wallbox. It is measured in mm² (cross-sectional area of the conductor). It is chosen, fitted and tested by a qualified installer. This is NOT something we sell, and it is not something you should size from a website.

The charging lead (a cable you plug in, measured in metres)

This is the Type 2 (or Type 1) lead that runs between your car and the charge point. Its "size" means LENGTH in metres and the current rating in amps. This is the part we make. If "size" means length for you, jump straight to our EV charging cable length guide or browse EV charging cables by car.

To be clear: we make EV charging cables (the lead), not the installation wiring. For the supply cable and the install, use a qualified EV installer.

EV supply cable size: a rule-of-thumb reference table

Use this table for orientation only. Every row is typical and must be confirmed by your electrician to BS 7671 for your specific installation. The run length bands below are illustrative because the real threshold shifts with install method, grouping and ambient temperature.

Notice there is no single "correct" number in that table, only typical starting points. A longer run often means going up a conductor size to keep voltage drop within BS 7671 limits, which is exactly why a calculator cannot give you a safe answer. For the single-output deep dives, see what size cable for a 7kW EV charger and what size cable for a 22kW EV charger.

What inputs does a real cable calculation use?

A proper BS 7671 calculation weighs several factors together. A web box that asks for one or two of them cannot be trusted. The real inputs include:

1. Load and current: a 7kW home wallbox draws 32A on single-phase 230V AC (7.4kW is the same thing rounded).
2. Run length: the total cable distance from the consumer unit to the wallbox, which drives voltage drop.
3. Installation method: clipped on a surface, in conduit, buried, or through insulation, each of which changes how much current the cable can safely carry.
4. Voltage drop: a longer run often means going up a size to stay within the regulations.
5. Grouping: whether the cable runs alongside other cables, which reduces its current capacity.
6. Ambient temperature: warmer surroundings lower the safe current rating.

Because these interact, two homes with the same 7kW charger can correctly need different cable sizes. That is the whole reason this work is left to an electrician.

Why can't I size it from a web box alone?

Sizing the supply cable wrong is a fire and shock risk, not a cosmetic choice. A calculator does not see your consumer unit, your cable route, how the cable is clipped or buried, or what else shares the run. It also cannot test the finished circuit. Under BS 7671 the installer does not just pick a number, they design the circuit, select protective devices, then test and certify it.

In England and Wales, installing or altering an EV charge point circuit is notifiable work under Part P. It must be done by a registered competent person, for example a firm registered with NICEIC, NAPIT or Stroma, or notified to building control. Scotland and Northern Ireland have their own equivalents. DIY is legal only if it fully complies and is notified and inspected, and it is strongly discouraged for EV circuits.

SWA or twin-and-earth: which supply cable type?

The cable type matters as much as the size, and again it is the installer's call.

SWA (steel-wire armoured)

SWA is used for outdoor, buried or exposed runs because the steel armour gives mechanical protection. Buried cable must be at an adequate depth with warning tape and suitable mechanical protection per the regulations. Your installer sets the depth and protection for your route.

Twin-and-earth (T&E)

T&E is only for protected indoor runs. It should not be used where it could be damaged or exposed to the weather. Many installs use a mix: T&E inside a protected route, transitioning to SWA where the cable goes outside or underground.

What about 22kW and three-phase at home?

22kW charging is three-phase, roughly 32A per phase. Most UK homes are single-phase, so they cannot run 22kW at home without a three-phase supply upgrade, which is uncommon, expensive and needs the DNO (Distribution Network Operator) involved. For most homes a 7kW charger is the sensible choice. If you are weighing the two, read 7kW vs 22kW, do I need a 22kW cable, and single-phase vs three-phase EV charging. For the 6mm² versus 10mm² question specifically, see 6mm vs 10mm cable for an EV charger.

What else does the installer sort out?

A few things commonly come up on the day, and they affect whether your supply can even take the charger.

The installer notifies the DNO for an EV charge point. Some supplies or higher outputs need prior approval before work, which can add time. If your main fuse or supply cannot take the extra load of around 32A, the installer may fit a CT-clamp load manager so the charger backs off when the house is drawing heavily, rather than upgrading the supply. For a walk-through of the visit, see EV home charger installation: what to expect.

Support exists for some households, for example flats, renters and landlords in certain cases. Amounts and eligibility change, so check gov.uk for current EV chargepoint grants rather than relying on a figure you read elsewhere.

If "size" means the charging lead, this is the easy bit

If you already have a charge point and you just want the lead, "size" means length and connector type, and you can choose that yourself. As a rule of thumb, 5m suits most driveways, while 7.5m or 10m helps with awkward parking or on-street setups. Match the lead to your car's inlet (Type 1 or Type 2) and current rating. A longer or heavier lead never makes the car charge faster than its onboard limit. Start with our length guide or see all our EV charging guides.

Frequently asked questions

Is there an EV charger cable size calculator I can trust?

No web calculator can safely size your supply cable, because the correct size depends on run length, installation method, grouping, ambient temperature and voltage drop. Use the reference table for a typical starting point, then have a qualified electrician confirm the size to BS 7671.

What size cable for a 7kW EV charger?

A 7kW charger draws 32A on single-phase. 6mm² is common for ordinary run lengths and 10mm² is often used for longer runs, but this is typical only and must be confirmed by your electrician to BS 7671 for your installation.

Can I use a cable size chart instead of an electrician?

A chart is useful for orientation, but it cannot replace an electrician. The installer designs the circuit, selects the protection, fits the cable and then tests and certifies it, which a chart cannot do.

Do I need SWA or twin-and-earth cable?

SWA is used for outdoor, buried or exposed runs because its steel armour protects it. Twin-and-earth is only for protected indoor runs. Your installer decides the type and route for your home.

Can I install the EV charger supply cable myself?

In England and Wales this is notifiable work under Part P, so it must be done by a registered competent person or notified to building control. Scotland and Northern Ireland have their own equivalents. DIY is strongly discouraged for EV circuits.

What length charging lead should I buy?

5m suits most driveways, while 7.5m or 10m helps with awkward parking. Match the connector to your car's inlet and current rating. See our length guide and shop charging cables by car.