How it’s calculated
The basic formula is the U.S. Department of Energy’s, and it’s the same one your utility uses:
kWh per day = appliance power (W) × hours used per day ÷ 1,000
A 90 W pedestal fan running 8 hours uses 90 × 8 ÷ 1,000 = 0.72 kWh per day, about 21.6 kWh per month.
The calculator adds one more input, the % of time running, because appliances with a thermostat (fridges, air conditioners, ovens, irons) aren’t at full power all the time: they switch on and off to hold the temperature. A 150 W fridge that runs half the time uses 150 × 24 × 0.5 ÷ 1,000 = 1.8 kWh per day.
What’s a watt, and what’s a kWh?
A watt (W) measures power: how much electricity an appliance uses at any given moment. A kilowatt-hour (kWh) measures energy: how much it uses over time. Think of a car’s speed (power) and the miles it covers (energy). Your bill charges for kWh: a 1,000 W appliance running for one hour uses 1 kWh.
Which units you can enter
- W or kW: whatever the label says. 1 kW is 1,000 W.
- Amps (A): if the label only lists amps, the calculator multiplies them by your home’s voltage (about 110–127 V in the United States, Canada and Mexico; 220–240 V in the UK, Ireland, Australia and most of Europe). 5 A at 120 V is 600 W.
- HP: the rating of motors, such as a water pump. 1 HP is 745.7 W. Note that it’s what the motor delivers; what it draws is usually a bit more.
- kWh per year: the figure on the energy label of fridges, freezers and washing machines. It’s the most reliable number for those appliances, because it already includes the on-off cycles.
Air conditioners: BTUs aren’t what it uses
BTUs (or frigories, used in Argentina and Uruguay) measure how much an air conditioner cools, not how much electricity it draws. One frigorie per hour is about 3.97 BTU per hour. To go from BTUs to watts you divide by the unit’s efficiency (its EER): a 12,000 BTU unit with an EER of 12 draws 12,000 ÷ 12 = 1,000 W. That’s why an inverter model of the same size uses noticeably less. To find what size you need for your room, use the air conditioner size calculator.
Where the appliance list comes from
Most appliances come from the official “basic appliance consumption” table published by ENRE, Argentina’s electricity regulator, which gives each appliance’s power and what it uses in an hour of use. That’s also where the % running for appliances with a thermostat comes from. A few older appliances (16 cu ft fridge, CRT monitor, VCR, dehumidifier) come from the U.S. Department of Energy table. Incandescent bulbs carry their wattage in their name. Electric showers aren’t in either table: the 5,500 W is a common label value, and it’s worth checking yours.
| Appliance | Power | Running |
|---|---|---|
| Fridge-freezer | 200 W | 45% |
| Fridge-freezer, inverter | 200 W | 17.5% |
| Air conditioner, 2,200 frigories | 1,350 W | 75% |
| Air conditioner, 2,200 frigories, inverter | 877.5 W | 75% |
| Automatic washing machine, 5 kg | 500 W | 35% |
| Clothes iron | 1,500 W | 50% |
| CRT TV, 29" to 34" | 175 W | 100% |
| LED TV, 32" to 50" | 90 W | 100% |
| Halogen / LED bulb | 60 W / 9 W | 100% |
| Older frost-free fridge, 16 cu ft (U.S.) | 725 W | 33% |
The two sources don’t always agree: ENRE counts a fridge as running about half the time, while the Department of Energy suggests one third. It depends on the model, the climate and how often the door is opened. If you want the exact figure for yours, use the kWh per year on its energy label or measure it with a plug-in energy monitor.
Why your bill may not match
- Some appliances are missing: devices on standby (TV, set-top box, a microwave with a clock) also use some power.
- Many utilities charge more per kWh above a certain usage (tiered rates), or depending on the time of day.
- Your bill adds fixed charges and taxes that don’t depend on how much you use.
Sources
- Ente Nacional Regulador del Gas y la Electricidad (Argentina). Consumo básico de electrodomésticos (in Spanish).
- U.S. Department of Energy, Energy Saver. Estimating Appliance and Home Electronic Energy Use.
- Virginia Cooperative Extension (Virginia Tech), 2020. Energy Series: Estimating Appliance and Home Electronic Energy Use (typical wattage table).