Power Converters
Last updated: 2 June 2026
| From | To |
|---|
Guide
Power: Kilowatts, Horsepower, and Your Electricity Bill
An air conditioning unit is rated "9kW cooling". Your car is advertised as "200 hp". A solar panel system is "6kW". Your electricity bill shows you used "15 kWh yesterday". These all relate to power, but they're measuring different things in different ways, and misunderstanding them costs real money on energy bills and on car purchases.
Start with watts. One watt is one joule of energy per second. One kilowatt (kW) is 1,000 watts. This is the rate at which something uses or produces energy right now. Your kettle might use 2,000 watts (2 kW) when you turn it on. Your fridge uses maybe 150 watts continuously. If you look at your electricity meter, it shows current power consumption. A 5-minute shower with an electric hot water system might use 5 kW.
Kilowatt-hours (kWh) are different. This is energy used over time. One kilowatt-hour is 1 kilowatt running for 1 hour. If your kettle uses 2 kW and runs for 20 minutes, that's 2 kW times 0.33 hours = 0.66 kWh. Your electricity bill charges you per kilowatt-hour. Australian electricity typically costs $0.28-$0.35 per kWh, varying by state. A 6 kW solar system producing all day might generate 30-40 kWh on a sunny day. This is why solar is worthwhile: it avoids buying 30-40 kWh from the grid at $0.30 each, saving roughly $9 per sunny day.
Horsepower (hp) is still used for cars, particularly when comparing old vehicles or imported cars. One horsepower is roughly 746 watts. A 200 hp car is about 149 kilowatts. Modern Australian cars list power in kilowatts on the spec sheet. A Toyota Camry might be listed as "203 kW", which is about 272 hp. The confusing bit is that different countries measure hp slightly differently. Metric horsepower (PS, used in Germany and historically in some European cars) is 735.5 watts, not 746. If you see "PS", convert at 735.5 watts per PS. Most Australians buy American or Japanese cars, which use the 746-watt horsepower.
Air conditioning cooling capacity is rated in kilowatts. A "9kW air con" removes 9 kilowatts of heat from your room. This doesn't mean it uses 9kW of electricity. A good AC unit has a COP (coefficient of performance) around 3-4, meaning it moves 3-4 kilowatts of heat for every kilowatt of electricity consumed. So a 9kW cooling AC might use 2.25-3 kW of power. This is why modern ACs are so much more efficient than old ones, and why upgrading from a 10-year-old unit can halve your cooling costs.
Solar panels are rated by kilowatts. A "6kW solar system" means the panels can generate 6 kilowatts in perfect conditions. Real-world output on a sunny day is 70-85% of that, so roughly 4-5 kW. On cloudy days, maybe 20% of that. Over a full year in Melbourne, a 6kW system generates about 7,000-8,000 kWh annually. That saves roughly $2,000-$2,500 per year on electricity, assuming no storage battery. Add a 10 kWh battery and you can use solar generation in the evening, further increasing savings.
BTU (British Thermal Units) is still used for air conditioning in the US and some imported specifications. One BTU is the energy needed to heat 1 pound of water by 1 degree Fahrenheit. About 3,412 BTU equals 1 kWh. A 12,000 BTU air conditioner is roughly 3.5 kW cooling capacity. If you see BTU on a spec sheet, divide by 3,412 to get kWh per hour, or multiply by 0.293 to get watts.
Common Questions
What's the difference between watts and kilowatt-hours?
Watts (or kilowatts) is power right now. Kilowatt-hours is energy used over time. Your kettle uses 2,000 watts. If you run it for 20 minutes, that's 2 kW times 0.33 hours = 0.66 kWh. Your electricity bill charges you for kWh, not watts. A 2kW kettle costs about $0.20 per use at $0.30 per kWh.
How many kilowatts is 200 horsepower?
200 hp times 0.746 = 149 kW. One horsepower equals 746 watts. A 200 hp car is about 149 kilowatts. Australian cars list kW in specs. American cars use hp. To compare, divide kW by 0.746 to get hp. A 200 kW car is about 268 hp.
How much does it cost to run a 2kW air conditioner all day?
2 kW times 24 hours = 48 kWh per day. At $0.30 per kWh, that's $14.40 per day. But most AC units have an effective COP, so they use less energy than their rated capacity. Real-world cost is probably $6-$10 per day depending on temperature and how hard the system works.
What's a reasonable solar panel system size for an Australian home?
Typical homes use 10-15 kWh per day. A 5-6 kW solar system generates 20-25 kWh on a sunny day, covering most daytime use. Without storage, you need to use the power while the sun's shining. A 10 kWh battery adds $5,000-$8,000 but lets you use solar power at night. Calculate your actual usage (check your bill), then size accordingly.
Is a 9kW air conditioner expensive to run?
The rated capacity (9kW) is cooling power, not electricity consumption. The unit might use 2-3 kW of electricity depending on efficiency. Cost is roughly 2.5 kW times your local rate (usually $0.28-$0.35 per kWh). Running it 8 hours costs about $5.60-$7. Not cheap, but not devastating. Running it 24/7 in summer is expensive.
What does 12,000 BTU mean for an air conditioner?
BTU is an imperial unit. 12,000 BTU equals about 3.5 kW cooling capacity. If you see BTU on a spec sheet, divide by 3,412 to convert to kWh. Most Australian specs now use kilowatts directly, which is clearer. 9,000 BTU is roughly 2.6 kW. 18,000 BTU is roughly 5.3 kW.
How We Verify Our Conversions
Every converter on RefDat uses peer-reviewed conversion factors sourced from the International Bureau of Weights and Measures (BIPM), the National Institute of Standards and Technology (NIST), and the Australian National Measurement Institute (NMI). Temperature formulas follow the ITS-90 international temperature scale. Cooking measurements use Standards Australia definitions (AS 1766) where applicable. We cross-check against multiple authoritative sources and test every calculator both forwards and backwards before publishing. If you spot an error, let us know.