What you need to know
- Measure for long enough to capture normal cycling.
- Record both kWh and measurement duration.
- Plug-in meters are not suitable for every appliance or fixed circuit.
Use your own measurements
Use the linked BricoDato resource to check these inputs in your own situation. A plug-in electricity meter can turn an appliance estimate into real kWh, but the measurement period must represent normal operation.
Watts are not monthly consumption
Power tells you the rate of energy use at a moment. Monthly energy depends on how long the appliance runs and whether it cycles or changes load.
Measure a representative period
For fridges, dehumidifiers and other cycling loads, a short reading can mislead. Measure over a normal day or longer when practical.
Convert measured kWh into cost
Multiply the measured kWh by your effective energy price. If the measurement covers several days, divide by days before scaling to a month.
Respect meter limits
Check maximum current and power, earthing, plug type and manufacturer instructions. Do not use a plug-in meter on hard-wired appliances or loads beyond its rating.
A repeatable 24-hour energy measurement
A plug-in electricity meter can turn an appliance estimate into real kWh, but the measurement period must represent normal operation. Thermostatic cycles, standby and seasonal conditions affect the outcome.
Example to adapt
Suppose a suitable plug meter reads 0.9 kWh after a complete 24-hour day for an appliance. At an illustrative €0.20/kWh, the daily energy cost is €0.18. Repeating the measurement for seven comparable days gives a more useful average for variable loads than one short peak reading.
| Appliance type | Measurement period | Why |
|---|---|---|
| Kettle or microwave | Multiple normal uses | Short cycles vary by usage |
| Refrigerator | Several complete days | Compressor cycles are irregular |
| PC or TV | Realistic viewing/work session | Workload and standby change draw |
Checks before acting
- Confirm the plug meter supports the appliance voltage, current and load safely.
- Start with the meter reset and record both elapsed hours and cumulative kWh.
- Avoid combining standby, active and unrelated appliances without noting the boundary.
- Convert measured kWh to cost using the correct tariff hours when possible.
Final check
A plug-in meter should record cumulative kWh over a useful sample, not just instantaneous W. Fridges, washing machines and thermostatically controlled heaters have varying operating phases; a brief high reading can overstate their daily energy. Confirm socket compatibility, current rating and that the appliance can safely use a plug-in measuring device without adapters or altered wiring.
- Check the meter rating.
- Measure a normal usage period.
- Record kWh and time together.
- Do not use plug-in meters on incompatible or fixed loads.
Keep a small job sheet
Record wattmeter model, appliance, duration, total kWh, conditions and applicable tariff.
Turn the guide into a decision
Log duration, kWh and operating conditions, then derive average use for a cycle or day. Apply your real tariff to that measured total and repeat if the appliance has seasonal behaviour; never put a meter into fixed wiring or exceed its marked load.