Power Converter
Convert between watts, kilowatts, horsepower and BTU/hr — and calculate exactly what any appliance costs to run at UK electricity prices.
POWER CONVERTER
Electrical power
Mechanical & heat
🔌 Running cost calculator
Enter a power value to see running costs
Enter your local electricity price per kWh and currency symbol.
Enter a power value to see a real-world comparison
Common appliances — click to load
Step-by-step solution
Type a power value to see the conversion working
⚡ EV Charging speeds
Key power facts
⚡ Power (W) vs Energy (kWh)
Power is the rate of energy use. Energy is the total used over time. Your electricity bill charges for energy (kWh), not power.
Energy = Power × Time
A 2 kW kettle running for 3 minutes uses:
2 kW × (3/60) hr = 0.1 kWh
At 25p/kWh, that costs 2.5p per boil.
Real-world power values
Power Converter Explained
Core concepts, classroom applications, and plain-English explanations for all audiences.
Where you'll actually use this
Every car is listed with both horsepower (hp) and kilowatts (kW) in the spec sheet. Your electricity bill charges you in kilowatt-hours. Old lightbulbs were 60 W; their LED replacements do the same job at 9 W. Solar panel output is rated in kWp. Power conversion is one of the most practically useful unit conversions there is.
Worked example
"Your kettle says 2,000 W. How much does it cost to boil it for 3 minutes at 28p/kWh?"
Step 1: 2,000 W ÷ 1,000 = 2 kW
Step 2: 3 minutes = 3/60 = 0.05 hours
Step 3: 2 kW × 0.05 h = 0.1 kWh
Cost: 0.1 × 28p = 2.8p per boil
Tip: Power (kW) × time (hours) = energy used (kWh). That's what your energy meter measures.
Key conversions to know
- → 1 horsepower = 745.7 W: A 100 hp car engine = 74.57 kW. Electric car specs often quote kW directly.
- → Old 60 W bulb → 9 W LED: Same brightness, 85% less power. The watts dropped but the lumens stayed the same.
Common mistake
Confusing power (W/kW) with energy (kWh). Power is the rate of use. Energy is power × time. You pay for energy, not power.
Understanding Power: Watts, Kilowatts, and Your Energy Bills
Power is a fundamental concept in physics and everyday life, especially when it comes to electricity. Simply put, power is the rate at which energy is used or produced. Think of it like this: if energy is the total distance you travel, power is your speed. The faster you use energy, the higher the power.
The standard unit for power is the Watt (W), named after Scottish inventor James Watt. However, you'll often encounter larger units like kilowatts (kW), megawatts (MW), and even gigawatts (GW) when discussing everything from your kettle to a national power station. Understanding these units is key to making sense of your electricity bills, the performance of your appliances, and how quickly your electric vehicle (EV) charges.
On mathsolvers.io, our Power Converter helps you switch between these units effortlessly. It also provides a handy running cost calculator, showing you how much an appliance or EV charger costs to run per hour, day, or year, based on typical UK electricity prices (e.g., 25p per kilowatt-hour). This tool is designed to empower UK households worried about energy bills, EV drivers planning their charging, and GCSE Physics students grasping core concepts.
Common mistakes to avoid
- My kettle is 2000kW:Kilowatt (kW) is 1,000 Watts (W). A 2000kW kettle would be incredibly powerful, consuming as much electricity as a small town! Your kettle is likely 2000W. My kettle is 2000W or 2kW.
- My TV uses 100kWh:kWh (kilowatt-hour) is a unit of energy (power used over time), not instantaneous power. Your TV's power rating is in Watts (W) or kilowatts (kW). My TV uses 100W. If I watch it for 10 hours, it uses 1kWh of energy.
- My car has 100 horsepower, so that's 100 Watts:Horsepower (hp) is an older unit of power, not directly equivalent to Watts. One horsepower is approximately 746 Watts. My car has 100 horsepower, which is about 74,600W or 74.6kW.
- A 2kW heater won't cost much to run:High power appliances use a lot of energy very quickly. A 2kW heater uses 2 kilowatt-hours (kWh) of energy every hour it's on, which can quickly add up on your electricity bill. A 2kW heater uses 2kWh of energy every hour, costing 50p/hour at a typical UK electricity price of 25p/kWh.