Most advice about cutting an electricity bill focuses on switching off lights and unplugging chargers. Those are fine habits, but their real effect on the bill is small — and they often distract from where the money actually goes.
Anything that heats or cools uses more than almost everything else combined: air conditioning, water heating, electric heaters. Then the fridge, because it runs 24 hours. Lighting, screens and chargers together are a small fraction of the bill.
The formula
One line is all you need:
Monthly cost = (watts × hours per day ÷ 1000) × price per kWh × 30The part in brackets gives you kilowatt-hours (kWh) per day — the unit you are actually billed in.
Example: a 1200-watt air conditioner running 6 hours a day, at 0.20 per kWh:
(1200 × 6 ÷ 1000) × 0.20 × 30 = 43One appliance. Nothing else in the house comes close.
The price per kWh varies by country and often by consumption band. Take it from your own bill — look for a line mentioning "kWh" — and use it in every calculation here instead of the default.
Common appliances
Calculated at 0.20 per kWh. Substitute your own price to make the table accurate for your home.
| Appliance | Watts | Hours/day | Monthly cost |
|---|---|---|---|
| Air conditioner (12,000 BTU) | 1200 | 6 | 43.20 |
| Electric water heater | 2000 | 2 | 24.00 |
| Electric heater | 2000 | 4 | 48.00 |
| Fridge | 150 | 24 (cycling) | 10.80 |
| Washing machine | 500 | 1 | 3.00 |
| Electric oven | 2000 | 0.5 | 6.00 |
| Iron | 1500 | 0.3 | 2.70 |
| Desktop computer | 200 | 6 | 7.20 |
| 50" LED TV | 100 | 5 | 3.00 |
| Laptop | 60 | 6 | 2.16 |
| 10 LED bulbs | 90 | 5 | 2.70 |
| Router | 10 | 24 | 1.44 |
| Phone charger | 5 | 3 | 0.09 |
Three results that contradict intuition
First: the electric heater costs more than the air conditioner. Because it converts electricity directly into heat at 100% efficiency and no more. An air conditioner works as a heat pump — it moves heat rather than generating it — so each unit of electricity produces several units of heat. Direct electric heating is the most expensive way to heat anything.
Second: the fridge is not the biggest consumer despite never switching off. Its wattage is modest and the compressor cycles rather than running constantly. It still lands high because 24 hours is a large number.
Third: the phone charger is a rounding error. Nine cents a month. Unplugging chargers is a good safety habit, not an economy measure.
The general rule
Look at the table as a whole and one pattern emerges:
Anything that heats or cools consumes in kilowatts. Anything that processes information or emits light consumes in watts.
The difference is a factor of a thousand. Which is why lowering the air conditioning by two degrees saves more than switching off every light in the house.
Where your effort actually pays
Ordered by effect, not by ease:
- Set the air conditioner to 25 rather than 22. Each degree is roughly 5–7% of its consumption. Three degrees ≈ a fifth off the largest line on your bill.
- Cut water heating time. Three minutes less in the shower beats every small appliance combined.
- Clean the air conditioner filter. A dirty filter forces the unit to run longer for the same result.
- Wash cold. Most of a washing machine's consumption goes to heating water, not turning the drum.
- Close doors and windows while cooling. Obvious, and constantly ignored.
Check it yourself
The table above is an estimate. For your real numbers:
- Read the meter at a fixed time, then again 24 hours later. The difference is your daily kWh.
- Try one day without air conditioning and compare. The gap is its true cost in your home, not an estimate.
- Read the appliance label — actual wattage may differ from the table.
That measurement is worth half an hour of your time, because it turns guesswork into a number you can act on.
See also: how to choose the right air conditioner size.
Frequently asked questions
How do I calculate one appliance exactly?
Multiply its wattage by the hours you run it daily, divide by 1000 to get kilowatt-hours, then multiply by your price per kWh and by 30 for a month.
Where do I find an appliance's wattage?
On the metal label at the back or underneath, or in the manual. It is given in watts (W) or kilowatts (kW). If only amps are shown, multiply by the voltage — usually 230 — to get watts.
Does standby power really matter?
Yes, but less than commonly claimed. A modern device on standby draws roughly 0.5 to 3 watts. Across ten devices the total stays small next to one air conditioner running two hours.
What is usually the biggest consumer?
Anything that heats or cools — air conditioning, water heating, electric heaters — then the fridge, because it runs around the clock despite a modest wattage.
Does switching off lights make a difference?
A small one if they are LED. Ten 9-watt LEDs running five hours cost far less than a single hour of air conditioning. Put your effort into heating and cooling.
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