How to use this calculator
Read the appliance input watts from its label, or use a plug-in meter to measure average power. Enter scheduled hours and quantity. For a cycling appliance, duty cycle is the average share of rated power while scheduled. If you measured average watts, use 100% duty cycle.
The formula
Daily kWh = W ÷ 1,000 × hours × duty% ÷ 100 × quantity. Monthly cost = daily kWh × days × rate.
Worked example
A 100 W appliance used 5 hours per day at 100% duty uses 0.5 kWh daily. Over 30 days it uses 15 kWh. At a sample rate of 0.16 per kWh, that costs 2.40 in the chosen currency.
Assumptions and limitations
Standby use outside the scheduled hours is excluded. Refrigerators, heaters and variable-speed appliances may draw much less than nameplate watts on average. The annual figure repeats your chosen month 12 times.
Frequently asked questions
Should I use maximum or average watts?
Measured average watts are usually more representative. Set duty cycle to 100% when using average watts so the reduction is not counted twice.
How do I estimate a refrigerator?
An annual kWh label is often more useful than maximum watts. Divide annual kWh by 365 to approximate daily energy, or measure a complete day with a suitable energy meter.
Estimates only. Use your utility tariff and appliance energy label for more accurate inputs.