Power Calculator

Power is the rate at which energy is transferred or work is done. The headline formula is P = W ÷ t — work divided by time. The same amount of work done faster requires more power; done slower, less. Power is measured in Watts (W), where 1 W = 1 Joule per second.

This calculator solves for power, work, or time when the other two are known, and also converts the result into kilowatts (kW) and horsepower (hp). Use it for physics problems, sizing motors, comparing engine outputs, or estimating how long a process will take given a known energy budget and continuous power draw.

A construction worker uses a small electric hoist to lift a 250 kg pallet vertically by 4 m in 8 seconds. What power does the hoist need to deliver (ignoring friction)?

• Work done against gravity: W = mgh = 250 × 9.8 × 4 = 9,800 J
• Power: P = 9,800 ÷ 8 = 1,225 W
• In other units: about 1.225 kW or 1.64 hp

Another example: a 75 W LED bulb left on continuously for one day uses 75 × 86,400 = 6,480,000 J (1.8 kWh) — costing about $0.27 at typical electricity rates.

• Physics problems — finding power from work and time, or work from sustained power.
• Sizing motors and pumps — figuring out the watts needed to move a load at a target rate.
• Comparing engines or tools — translating between hp, kW, and W to compare specs across regions.
• Energy bill estimates — converting between continuous wattage and total kWh consumed.
• Athletic performance — calculating sustained power output during running, cycling, or lifting.

• Confusing kW with kWh. kW is power (a rate); kWh is total energy (a quantity). A 2 kW heater running for 3 hours uses 6 kWh.
• Mixing up horsepower types. Mechanical hp (745.7 W), metric hp (735.5 W), and electrical hp (746 W) are slightly different — this calculator uses mechanical hp.
• Ignoring efficiency. Real motors and engines convert input energy at less than 100%; output power is less than input.
• Using minutes or hours instead of seconds. Dividing Joules by minutes gives J/min, not Watts.
• Forgetting that power varies over time. P = W/t gives the average — peak power during a process can be much higher.