Measuring electricity and standby use with a plug-in meter

Start with something you can safely switch off temporarily, such as a desk lamp or television. Do not interrupt medical equipment, alarms or other essential services for a measurement. Avoid moving heavy appliances to reach their plugs. Hard-wired appliances and measurements inside the consumer unit are outside this guide.

Understand what the display measures

Watts, written W, describe power at a particular moment. Kilowatt-hours, written kWh, measure accumulated energy. A lamp drawing 10 W for 10 hours consumes 0.1 kWh. The calculation is W ÷ 1000 × hours.

A meter with a kWh register accumulates changing consumption during the measurement. That gives a better basis for an estimate than multiplying one instantaneous reading by an entire year. Record the circumstances too: perhaps 4 evenings watching television and 3 evenings away. An unusual week makes a poor guide to your normal annual use.

Equipment and purchasing checklist

Compare a suitable model at Praxis (SUP-010) and GAMMA's energy-meter category. Look for a plug-in consumer product. A DIN-rail meter intended for a consumer unit is a different product requiring installation work.

Do not judge compatibility from a maximum wattage alone. Motors and starting currents may have separate restrictions. For its specified model, the Kopp meter manual prohibits chained meters and intermediate adaptors and restricts use to dry indoor spaces. Check the model number; the document does not approve every Kopp meter for your appliance.

Record a useful measurement

1. Choose one accessible, undamaged appliance. Look at its lead, plug and socket without opening anything. Do not begin if there is damage, discolouration or moisture.
2. Confirm that both sets of instructions permit the arrangement. Shut the appliance down correctly before inserting the meter. Connect the meter directly to the wall socket without stacked adaptors.
3. Clear the previous measurement using the meter's instructions. Write down the starting time. Check that you are reading kWh rather than W or a cost display.
4. Use the appliance normally. Include complete usage periods, such as several evenings of television with the standby periods between them.
5. Record the final reading and elapsed time. Stop if there is unusual heat, looseness, noise, smoke or a smell. Keep clear of a damaged or hot connection and arrange help.

Smoke, fire or immediate danger? Move to safety immediately and call 112. Do not go back inside. Do not wait for a contact-form response or collect more readings. For an irregularity without immediate danger, leave the appliance out of use until appropriate help has assessed the cause. Veiligheidsregio Zuid-Holland Zuid on responding to fire.

For a separate standby measurement, put a suitable appliance into standby using its normal controls. A zero on the meter does not prove absolutely zero consumption: the instrument's resolution and accuracy limit what it can display.

Worked example from a measurement week

Suppose a television consumes 2.4 kWh during 7 representative days. At an example rate of €0.30 per kWh, the week's energy cost is 2.4 × 0.30 = €0.72. Annualising it gives 2.4 ÷ 7 × 365 = 125.1 kWh, costing approximately €37.54 at that same rate.

Choose Measured kWh in the calculator. Enter 2.4 kWh, 7 measurement days, 365 projection days and your own tariff. The result remains an estimate based on a representative measurement period.

That calculation assumes the same pattern all year. With a dynamic electricity contract, one average rate is only an approximation. Holiday periods and changes in viewing habits alter the result. The measurement also tells you nothing about whether the socket's wiring is safe.

Common questions

Can I measure a fridge? Only if the meter permits the exact load type and both manufacturers' instructions allow the arrangement. Get advice if you are unsure about the compressor, access or restart requirements. A lamp is an easier first measurement.

Does a smart plug always save energy? No. It consumes electricity itself. Any saving depends on the equipment being switched off, the hours avoided and the smart plug's own consumption.

Should everything be off overnight? Decide which functions must remain available before changing anything. Refrigeration, security, communications and medical equipment need their own assessment.

If your consumption remains unexplained or you need to assess fixed equipment, ask CAS Elektrotechniek to review the situation. Include the measurement period, readings and usage notes so the conversation starts with useful evidence.

Sources

Checked on 5 October 2026: Milieu Centraal, standby consumption and the model-specific Kopp meter manual. Calculations use illustrative readings and electricity prices.