Appliance electricity use: the calculation step by step

The formula, and its three traps

Consumption in kWh = power in kW × time in hours. To go from watts to kilowatts, divide by 1,000: 1,500 W is 1.5 kW. For a time in minutes, divide by 60: 30 minutes is 0.5 hours. A 1.5 kW appliance used for 30 minutes therefore uses 0.75 kWh.

The first trap is thermostat appliances. An oven, a radiator, a water heater or a washing machine heats at full power, stops, then starts again: the plate shows a maximum, not an average. The calculation then gives a ceiling, not real consumption. The second trap is time: people readily overestimate a dryer’s running time and forget an appliance that never switches off. The third is standby, the few watts drawn around the clock by appliances that are “off”.

A few worked examples

The table applies the formula to powers and times chosen as examples, at the prices of the Tarif Bleu grid of 1 August 2026. Swap in your own appliances in the mini-calculator.

The last column is a reminder of what each kWh costs on a Tempo red day between 06:00 and 22:00: an appliance used at those hours on those days costs more than three and a half times its Base price. That is why “when” matters as much as “how much” once you choose Tempo.

Standby, small but constant

An appliance on standby draws little, but 24 hours a day, 8,760 hours a year:

Add up the internet box, the TV decoder, the console, the computer and chargers left plugged in, and the total becomes noticeable over a year. Switching off what is not in use, with a switched power strip, costs no comfort.

From one appliance to the whole home

Adding up every appliance to rebuild your annual consumption is tedious and often wrong, because real running times are poorly known. Your bill, or your supplier’s online account, gives the total directly, and the Linky meter breaks it down half-hour by half-hour. The per-appliance calculation serves another purpose: deciding where to put the effort and knowing what to move into off-peak hours.

If several big appliances can run at night, compare the options: on Off-peak a night-time kWh costs €0.1589; on Tempo, €0.1356 on a blue day, within the 22:00 to 06:00 window set by the tariff. The Base, Off-peak or Tempo comparison works it out on your total consumption.

Appliance power and meter power

Each appliance’s power also helps choose the meter power: the total of what runs at the same time must not exceed the subscribed kVA, or the breaker trips. An oven, a hob, a dryer and the heating on together can exceed 9 kW. The meter power page adds up your appliances and gives the recommended power, with the matching standing charge from the regulator’s tariff proposal.

Comparing two appliances before buying

The formula also helps compare two appliances. Two models that do the same job can be told apart by their annual consumption multiplied by the years you will keep them. A gap of 100 kWh a year comes to €20 a year on Base at 6 kVA, or €200 over ten years at today’s prices. For appliances sold with an energy label, the standardised annual consumption printed on it allows this sum directly; for the others, start from the power and your real use.

The same reasoning applies to timing. On Off-peak, a kWh moved from daytime to night saves €0.0553; on Tempo, a kWh moved from red peak hours to the night saves €0.5680. That is why the same appliance can cost almost the same in two households on the same option, and very differently in two households with different habits.

What the calculation does not tell you

The cost worked out here is for energy alone. The standing charge, paid whatever you use, does not change because an appliance runs an extra hour; it only moves with the meter power. The calculation also ignores wear, maintenance and purchase price. Finally, an appliance that gives off heat indoors, such as an oven or a tumble dryer, slightly eases the heating’s work in winter: a real effect but a hard one to put a figure on, which this site does not model.

From kVA to kW and back

Meter power is expressed in kilovolt-amperes (kVA), appliance power in watts or kilowatts. For household use you can treat one kVA as roughly one kW: a 9 kVA meter carries about 9 kW of appliances switched on at the same time. That approximation is enough to choose your power; it plays no part in working out consumption, which depends only on the kilowatt-hours actually used.

The Linky meter lets you check all this: it shows the power being drawn at any moment, and the supplier’s online account gives consumption by half-hour. Switching an appliance on by itself and watching how far the displayed power rises is the simplest way to find its real power when the plate is unreadable or missing.

For an appliance plugged in all the time, such as a fridge or freezer, the most accurate approach is to measure its use over a whole week with a plug-in meter and multiply by 52: the compressor stops and starts, and a one-hour reading says almost nothing.

If you have just moved to France, note that appliances bought elsewhere in Europe use the same 230 V supply, so their rating plates read the same way and the formula applies unchanged.

One last tip on method: write your sums down. A list of your hungriest appliances, with their power, running time and annual use, comes in handy at every change: buying a new appliance, switching option, an electric car or heat pump arriving. Comparing it with the bill’s total also shows whether something has been forgotten, such as a back-up water heater, an aquarium or a pool pump running without anyone noticing. Keep the list with your bills and update it when the tariff changes: the kWh stay the same, only the prices move.