How to Measure Appliance Energy Use: Four Methods, Step by Step

To measure appliance energy use, plug the appliance into a plug-in energy meter or a smart plug with energy monitoring and leave it running through a normal day or week; the kWh total is what it really uses. For hard-wired appliances, use your electricity meter or smart meter display and compare readings before and after use. The energy label gives a useful estimate before you buy, but only a measurement tells you what the appliance uses in your home, used your way.

The two numbers you are measuring

Every method below gives you one or both of these:

• Power, in watts (W): how hard the appliance is drawing electricity right now. A kettle might draw around 3,000 W while boiling; a laptop charger perhaps a few tens of watts.
• Energy, in kilowatt-hours (kWh): power multiplied by time. This is what your bill charges for. One kWh is 1,000 W for one hour, or 100 W for ten hours.

The link between them is simple: kWh = watts × hours ÷ 1,000. Then cost = kWh × your unit rate. At the Ofgem price cap average for October to December 2026, that rate is 26.32p per kWh for Direct Debit customers in England, Scotland and Wales; the EU household average was around €0.28 per kWh in the first half of 2026, according to Eurostat figures reported by the Brussels Times. For the full method with worked examples, see how to calculate the running cost of an appliance.

Power on its own can mislead. An appliance that cycles (a fridge, a dryer's heater, an oven thermostat) jumps between high and low draw, so a single live reading tells you little. Energy over time is what matters.

Method 1: read the energy label and rating plate

Best for: comparing appliances before you buy.

Since March 2021, fridges and freezers, washing machines, washer-dryers, dishwashers, TVs and monitors have carried the rescaled A–G energy label. The label includes a consumption figure measured under standard test conditions:

• Fridges and freezers: kWh per year.
• Washing machines and dishwashers: kWh per 100 cycles (divide by 100 for a single cycle on the test programme).
• TVs and monitors: kWh per 1,000 hours of use.

The rating plate (usually on the back or inside the door) shows something different: the maximum power the appliance can draw. It is useful for checking an appliance is within a socket's or smart plug's rating, but it overstates typical use for anything that cycles.

Limitations: test conditions are not your kitchen. Programme choice, temperature, how full you load it, room temperature and age all change real use. Labels also do not exist for many small appliances.

Method 2: a plug-in energy meter

Best for: a quick, accurate check on any plug-in appliance.

A plug-in energy meter is a small adapter with a display that sits between the wall socket and the appliance. It shows live watts and accumulates kWh.

1. Plug the meter into the wall, then the appliance into the meter.
2. Reset the kWh counter.
3. Use the appliance normally for the measurement period.
4. Read the total kWh at the end.

Limitations: you have to go and read the display, history is usually limited, and you can only measure one thing at a time per meter.

Method 3: a smart plug with energy monitoring

Best for: measuring over days or weeks without visiting the socket, and acting on the results.

A smart plug that monitors energy works like a plug-in meter but sends the readings to an app. You see live watts and a running history, often as daily, weekly and monthly charts, and you can switch the appliance on and off or schedule it. This makes it much easier to measure a fridge for a full week, see what a games console does overnight, or compare the cost of two washing programmes. Our guide to smart plug energy monitoring explains what the readings mean and what affects accuracy.

Limitations: it needs Wi-Fi (or a hub, for Zigbee models) for live data; it uses a little power itself; it only measures what is plugged into it; and you must stay within its current rating.

Method 4: your electricity meter or smart meter

Best for: hard-wired appliances and checking your whole-home background load.

Electric showers, ovens, hobs, immersion heaters, storage heaters and ceiling lights are wired in, so nothing that goes into a socket can measure them. Your meter can.

With a smart meter in-home display (IHD): the display shows your whole home's use in near-real time. Watch the live figure, switch the appliance on, and note the jump. For energy, note the day's kWh before and after a session.

With a standard meter: take a reading, run the appliance for a known time with as little else running as possible, and take another reading. The difference is approximately what the appliance used, plus whatever else was running.

Limitations: other appliances add noise, especially fridges switching on, so repeat the test two or three times. The smart meter vs smart plug question is covered in depth in smart plug vs smart meter.

Comparison: which method to use

Step by step: measuring one appliance properly

1. Decide the question. "How much does my tumble dryer cost per load?" needs a different test from "How much does my fridge-freezer cost per year?"
2. Choose the measurement period. One full cycle for washing machines, dishwashers and dryers. At least 24 hours, ideally seven days, for fridges and freezers. A typical week for TVs, computers and consoles.
3. Check the rating. Make sure the appliance's maximum power is within the meter's or smart plug's rating. Never put a high-power heater on a device rated for less.
4. Connect and reset. Plug the meter or smart plug in, connect the appliance, and reset or note the starting kWh.
5. Use it normally. Do not change your habits during the test, or you will measure a version of your home that does not exist.
6. Record the total kWh and the period it covers.
7. Scale it up. Multiply a week by 52 for a yearly figure, or a cycle by the number of cycles you run a year.
8. Convert to cost with your unit rate.
9. Change one thing and measure again. Try a lower temperature, a shorter programme or a schedule, and compare.

A worked example (hypothetical)

Say a fridge-freezer uses 7.0 kWh over a measured week. That is 7.0 × 52 = 364 kWh a year. At 26.32p per kWh, that is 364 × £0.2632 = about £95.80 a year. If its energy label claims 250 kWh a year, the difference is worth investigating: check door seals, temperature settings and whether it sits next to a heat source.

Common mistakes

• Taking one live reading and multiplying by 24. A fridge's compressor might show 100 W one minute and near zero the next. Measure energy over time.
• Measuring too briefly. Ten minutes of a washing machine misses the heating phase or the spin.
• Daisy-chaining meters or plugs. Plug one device directly into the wall.
• Ignoring the rating. Space heaters, dryers and kettles draw a lot. Check the plug and socket can handle them.
• Forgetting the rest of the bill. Measurement covers usage, not the fixed daily standing charge.

Where Wattly fits (and where it doesn't)

A Wattly smart plug is a Method 3 tool. It shows live watts, cost per hour, day, week and month, and usage history in daily, weekly, monthly and yearly charts in the Tuya Smart app, so you can leave it on an appliance for a week and look at the result from your phone. Then you can use its schedules, timers and remote on/off to act on what you find.

It cannot measure hard-wired appliances, and it is not a whole-home meter. For high-power appliances, stay within its rating: 13 A for the UK Type G version; 16 A (3,680 W) or 20 A (4,600 W) for the EU Schuko versions. If you only want a one-off reading, a basic plug-in meter does that job too. See the Wattly product page for versions.

Related reading

• What uses the most electricity at home
• Standby power explained
• How to calculate appliance running cost
• Tuya and Smart Life smart plug setup