Power Calculator

Power vs Energy (They're Not the Same)

Energy is the total amount of work done (Joules). Power is how fast you do it (Watts = Joules/second). A 100W light bulb and a 10W light bulb both use energy, but the 100W bulb burns through it 10× faster. That's power.

Kilowatts are Just 1000 Watts

Electric companies bill in kilowatt-hours (kWh). That's power × time. If you run a 1000W (1 kW) microwave for 1 hour, you use 1 kWh of energy. Most houses use 20-30 kWh per day. Your electric bill is basically "how many kWh did you use this month?"

Horsepower is Outdated But We're Stuck With It

1 horsepower ≈ 746 Watts. It's a weird unit (based on how much power a horse can sustain), but car companies still use it because people understand "200 horsepower" better than "150 kilowatts." Both mean the same thing though.

Confusing Power and Energy

"My phone battery has 5000 mAh so that's the power." No - that's energy capacity. Power is how fast you use that energy. A 5W charger takes forever to fill a battery. A 20W fast charger does the same work in 1/4 the time. Same energy, different power.

Why it matters: You'll get confused reading your electric bill or comparing chargers.
Fix: Energy = total work (Joules, watt-hours). Power = how fast (Watts).

Mixing Up Units

Work needs to be in Joules, time in seconds. You can't use kilowatt-hours for work and minutes for time - the math falls apart. Convert everything to base SI units (Joules, seconds) before calculating.

Real consequence: Your answer is off by factors of 60, 1000, or worse.
Fix: Always convert to Joules and seconds first.

Thinking Higher Wattage is Always Better

A 1500W space heater isn't "better" than a 1000W heater if you only need 500W of heat - you're just wasting electricity. Higher power = faster/more intense, but that's not always what you need. Match the power to the task.

How to avoid: More Watts = more energy used per second. Only go higher if you need faster results.

What is power in physics?

Power is how fast work gets done. It's work divided by time (P = W/t). If you lift 100 Joules worth of stuff in 5 seconds, your power output is 20 Watts. Do the same work in 2 seconds? Now you're at 50 Watts. Same work, less time, more power.

What is a Watt?

A Watt is 1 Joule per second. It measures power - how fast energy is used or transferred. A 100W light bulb uses 100 Joules of energy every second. Your microwave? Maybe 1000W (1 kilowatt). A car engine? 100,000W or more (100+ kilowatts or ~134 horsepower).

How do you calculate power from work and time?

Divide work by time: P = W/t. Example: You do 500 Joules of work in 10 seconds. Power = 500÷10 = 50 Watts. More work in the same time = more power. Same work in less time = more power. That's the whole formula.

What's the difference between energy and power?

Energy is the total work done (measured in Joules). Power is how fast that work gets done (measured in Watts). Running up stairs uses the same energy whether you walk or sprint - but sprinting requires more power because you're doing it faster.

How many Watts is a horsepower?

1 horsepower = 746 Watts (roughly 750W). A 200 horsepower car engine produces about 150,000 Watts. Engineers originally defined horsepower based on how much power a horse could sustain - turns out it's pretty arbitrary, but we're stuck with it.