Electricity & energy

Measure energy, not just rated power

Rated power tells you the maximum or nominal electrical load of an appliance, but it does not tell you how much energy it will use over a day, month or year. Real consumption depends on power, operating time, thermostat cycles, standby use and how the appliance is actually used.

For a quick estimate, multiply watts by hours of use and divide by 1,000 to get kWh. Then multiply the result by your electricity price. This is useful for comparing options, but a plug-in energy meter is better when the appliance cycles on and off or has variable power.

A practical way to compare appliances

• Start with the appliance power in watts.
• Estimate realistic daily operating time rather than assuming it runs at full power continuously.
• Convert the result to kWh and use the price you actually pay for electricity.
• For fridges, heat pumps, air conditioners and similar equipment, use measured consumption whenever possible because compressor cycles matter.
• Compare annual running cost as well as purchase price when choosing between efficient and less efficient equipment.

What usually makes the biggest difference

Heating and cooling loads, water heating and appliances used for many hours usually matter more than small standby loads. Lighting can still add up across many fittings, which is why replacing halogen lamps with LED is often easy to quantify.

Use BricoDato's electricity consumption calculator to turn watts and hours into cost, check the appliance consumption library for typical examples, and compare lighting choices with LED vs halogen.

Tip: when an estimate and a measured value disagree, trust the measurement first and then check whether your assumed operating hours or power level were realistic.