Every UK 13A extension lead has a hard ceiling of about 3,000W (13A at the UK's 230V nominal supply) — and cable reels drop to roughly half that when coiled, because a wound cable can't shed heat. Tick the appliances you plan to plug in and this calculator shows whether the combination is safe.
What will you plug in?
Tick appliances above to see the total load.
The UK rules behind the numbers
- 13A plug = ~3,000W maximum for the whole lead at the UK's 230V nominal supply (BS 1363 plugs and sockets; supply voltage per BS 7671). A 4-way lead does not mean 4 × 13A.
- Cable reels roughly halve when coiled. A typical 13A reel is rated around 6–7A wound — check the reel's printed coiled/uncoiled ratings and always fully unwind for heavy loads. Browse cassette & cable reels with thermal cut-outs.
- Never daisy-chain extension leads, and keep heaters, kettles and irons on wall sockets where possible — or add proper sockets instead: see upgrading your sockets.
- Outdoors: use RCD protection and the right IP rating — RCD leads and our IP ratings guide.
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