What you need to know
- Convert W to kW before multiplying by hours.
- Appliances with cycles do not run at maximum power all the time.
- Keep the energy cost separate from other items on the electricity bill.
Run the calculation with your own data
The guide explains the formula; the calculator does the arithmetic.
The basic formula
Convert W to kW by dividing by 1,000. Multiply by hours of use to get kWh, then multiply by the price per kWh.
Load factor
Thermostats, compressors and power electronics mean many appliances do not run continuously at maximum power. A load factor can make the estimate more realistic.
Daily, monthly and annual cost
Do not extrapolate occasional use without adjusting the frequency. If an appliance is used 20 times a month, calculate that pattern rather than assuming 30 days.
What the estimate does not include
The calculated cost represents energy use. Your bill may also include contracted power, taxes, meter rental and other charges.
BricoDato tip
Use measured values and manufacturer data whenever possible. If you need a margin, make it explicit rather than rounding by eye so you can repeat the calculation and compare alternatives.
Checklist before buying
- Check the real measurements or power ratings.
- Check the product technical data sheet.
- Add a reasonable margin, not an arbitrary one.
- Save the result and compare it with the actual product or tariff format.
Mistakes to avoid
Do not use a generic value when the manufacturer provides a specific one. Match the calculation to the real usage pattern and check whether conditions change the estimate.
Frequently asked questions
Can I use the result as a fixed quote?
No. It is an estimate for planning consumption or cost. Use real prices and conditions before making a purchase or commitment.
What if my result sits between two values?
Consider the cost of underestimating against the value of any reusable surplus. For products sold in fixed quantities, avoid assumptions that hide the real purchase size.
Final check
Before accepting the result, review these points to catch measurement, interpretation or safety errors.
- Distinguish W from kWh
- Measure complete cycles when a thermostat is involved
- Use a consistent energy price
- Repeat the measurement if the usage pattern changes significantly
Record these details so you can repeat the calculation
An estimate is much more useful when you can reproduce it. Save the appliance model, rated or measured power, hours/minutes of use, resulting kWh and the energy price used. If the appliance has several modes, record them separately.
When comparing two periods, keep the conditions as similar as possible. For climate control, note outdoor temperature and setpoint; for a PC, workload; for lighting, operating hours. This prevents you from attributing a difference to the wrong cause.
Turn the guide into a decision
Use your measurements, the product data sheet and the real conditions in your home. If a decision affects safety, fixed installations or a fault you cannot identify, consult a professional.