What Size Cable for a Cooker? UK Guide (2026)

The first thing that trips people up is that a cooker's cable is not sized for its full nameplate rating. A cooker never has every ring, the oven and the grill flat out at once, so BS 7671 and the IET On-Site Guide allow you to apply diversity to household cooking appliances. The recognised method is to take the first 10 amps of the appliance's full load current, add 30% of the remainder, and add a further 5 amps if the cooker control unit includes a socket outlet.

Take a 12 kW range cooker on a 230 volt supply. Its full load current is 12,000 divided by 230, which is about 52 amps. Apply diversity: 10 amps, plus 30% of the remaining 42 amps which is 12.6 amps, plus 5 amps for a switch with a socket, gives a design current of about 28 amps. That is the figure the circuit is actually built around, not the 52 amps on the rating plate.

Takeaway: size a cooker circuit from its diversified design current, usually around 25 to 32 amps for a domestic cooker, not from the full nameplate load.

Once you have the design current, the protective device has to sit above it and below the cable's capacity. For a diversified cooker load of around 28 amps, a 32 amp MCB is the standard choice, because its rating is comfortably above the design current so it will not trip in normal use. A very large range cooker with a diversified load above 32 amps may need a 40 amp device and a bigger cable to match. A single built-in oven on its own, rather than a full cooker, often draws little enough to run from a 16 or 20 amp circuit, though many electricians still put it on a dedicated cooker circuit for future-proofing.

Takeaway: match the MCB to the diversified load first, then size the cable to suit the MCB, in that order.

Here is where the forum answer falls apart. A 6mm² twin and earth cable can carry roughly 32 to 46 amps depending on how it is installed, and 10mm² carries more. The installed capacity, called the current-carrying capacity or Iz in BS 7671, drops sharply when the cable is surrounded by insulation, run with other cables, or buried in a wall rather than clipped on a surface. A 6mm² cable clipped directly to a joist in open air comfortably handles a 32 amp cooker circuit. The same cable buried in a thermally insulated wall, or run in the same trunking as several other circuits, can have its capacity pulled down close to or below 32 amps, at which point it is no longer adequate.

The second factor is length. Over a long run the cable's voltage drop grows, and BS 7671 limits the drop to 5% for this kind of circuit, which is 11.5 volts on a 230 volt supply. A 6mm² cable on a 32 amp load is usually fine up to somewhere around 15 to 20 metres, but past that the voltage drop can force you up to 10mm² even though the current alone would allow 6mm². This is exactly the calculation the Cable Sizing Calculator and the Voltage Drop Calculator are built to do.

Takeaway: 6mm² suits most short, well-ventilated cooker runs, but a long run or a cable smothered in insulation can push you to 10mm² regardless of the breaker.

Picture a new cooker circuit in a Bristol semi. The cooker is a 10 kW freestanding model, and the control switch has a socket. Its full load current is 10,000 divided by 230, about 43.5 amps. Apply diversity: 10, plus 30% of 33.5 which is 10 amps, plus 5 for the socket, giving a design current of about 25 amps. A 32 amp MCB sits nicely above that.

Now the cable. The run from the consumer unit to the cooker switch is 14 metres, clipped along the underside of the ground-floor joists and partly through a stud wall, so it is not smothered in insulation. Under those conditions 6mm² twin and earth has enough current capacity for the 32 amp breaker. Checking voltage drop, 6mm² has a drop of roughly 7.3 millivolts per amp per metre, so 25 amps over 14 metres gives about 2.6 volts, which is well inside the 11.5 volt limit. So 6mm² on a 32 amp MCB is correct here.

Change one thing, and the answer changes. If that same cable had to run 24 metres and pass through a loft packed with insulation, the reduced capacity and the higher voltage drop would push the specification to 10mm². The parts are cheap enough to get from Screwfix or a local City Electrical Factors branch, but the sizing is not a guess. It follows from the length and the install method.

Takeaway: for a typical short, ventilated cooker run, 6mm² on a 32 amp MCB is right. Change the length or bury it in insulation and you have to redo the sum.

Almost every "what size cable for a cooker" article stops at the cable and never mentions the law. A new cooker circuit is a fixed electrical installation in a kitchen, which is defined as a special location under Building Regulations. In England and Wales, adding a new circuit like this is notifiable under Part P of the Building Regulations. That means it either has to be done by an electrician registered with a competent person scheme such as NICEIC or NAPIT, who self-certifies it, or it has to be notified to your local authority Building Control before the work starts and inspected. Scotland has its own building standards, and the notification routes differ.

This matters for real reasons, not just paperwork. Uncertified electrical work can cause problems when you sell the house, can invalidate insurance after a fire, and skips the inspection that would catch an undersized cable or a poor connection. Replacing a cooker on an existing, sound circuit is not notifiable. Running a brand new circuit almost always is.

Takeaway: sizing the cable is the easy half. A new cooker circuit is notifiable under Part P in England and Wales, so it is a job for a registered electrician or one signed off by Building Control, not a DIY afternoon.

Work out the diversified design current, pick the MCB above it, then size the cable to the run and the install method rather than to a rule of thumb. Do the numbers with the Cable Sizing Calculator, check the run with the Voltage Drop Calculator, and if it is a new circuit, get a registered electrician to install and certify it.