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How to Measure Appliance Electricity Use in the UK

Learn how to measure appliance electricity use with a plug-in meter or smart plug, calculate the cost in pounds and avoid common mistakes.

Published 25 September 2026 · Last checked 26 September 2026

Quick answer

The most reliable way to measure appliance electricity use is to connect a suitable plug-in energy meter or UK energy-monitoring smart plug, run the appliance normally, record the kWh reading and multiply it by your electricity unit rate.

What you need

  • A plug-in electricity meter or energy-monitoring smart plug rated for the appliance load.
  • Your current electricity unit rate in pence per kWh, found on your bill or tariff information.
  • At least 24 hours of normal appliance use; several days is better for appliances that cycle on and off.

Basic method

  1. Check the appliance label and confirm that the meter or smart plug is rated for its maximum load.
  2. Connect the meter directly to a dry, accessible UK wall socket.
  3. Plug the appliance into the meter and reset the energy reading.
  4. Use the appliance normally for at least 24 hours.
  5. Record the total kWh shown.
  6. Multiply the kWh by your electricity unit rate to calculate the additional running cost.

Cost formula

Cost (£) = energy used (kWh) × electricity unit rate (£/kWh)

For example, 3.5kWh at 26p/kWh costs about 91p. This is the appliance’s additional electricity cost and does not add the daily standing charge, which is normally paid regardless of whether the appliance is running.

How long should you measure?

Measure for at least 24 hours for a basic estimate. A week gives a more useful average when the appliance uses different modes, responds to room conditions or cycles on and off, such as a dehumidifier, fridge or heating appliance. Divide the total cost by the number of days to estimate a daily average.

Common mistakes to avoid

  • Using the appliance’s rated wattage as though it runs at full power continuously.
  • Adding the standing charge to the appliance’s incremental cost.
  • Measuring only for a few minutes and treating the result as a normal daily average.
  • Using a smart plug without checking its maximum load and manufacturer instructions.
  • Placing electrical connections where they can become wet or exposed to condensation.

For a practical example, see how much a dehumidifier costs to run. You can also compare the best smart plugs with energy monitoring in the UK.