Power Calculator

Power is how fast energy is delivered or how quickly work gets done. Two machines might do the same total work, but the one that does it faster has more power. A 100-watt bulb uses the same energy in 10 seconds that a 10-watt bulb uses in 100 seconds. Power is the rate, not the total. There are two common ways to calculate mechanical power. The first takes the total energy transferred and divides by the time taken. The second multiplies the applied force by the velocity at which the object moves. Both arrive at watts, and both are physically equivalent. This calculator handles both methods. The energy-time approach is useful for engines, motors, and any scenario where you know total energy input and duration. The force-velocity approach suits situations like a car engine driving against drag or a cyclist applying force to pedals at a known cadence and gear ratio.

• Engine and motor selection: Determine the minimum power rating required for a motor to perform a given task within a time limit. Compare the calculated watts to motor datasheets.
• Athlete performance analysis: Elite cyclists sustain roughly 300 to 400 W for an hour. Enter force on the pedals and pedalling velocity to estimate an athlete's output power and compare across sessions.
• Elevator and hoist design: Calculate the power needed to lift a known load at a target speed using P = F × v, where F is the weight of the load and v is the lifting velocity.
• Energy consumption estimation: Multiply power in watts by time in hours to get watt-hours (energy used). This is how electricity meters work. Use the energy-time method in reverse to understand running costs.

• Entering energy in kJ instead of J: The energy input field expects joules. If you have a value in kilojoules, multiply by 1000 first. Entering 10 kJ as 10 (rather than 10,000) gives a power 1000 times too low.
• Confusing power and energy: Power is a rate (watts = joules per second). Energy is a total (joules). A 2000 W heater running for 1 hour uses 7,200,000 J (= 2 kWh) of energy. Watts alone tell you nothing about total consumption.
• Ignoring losses in real systems: This calculator gives ideal (theoretical) power with no friction or inefficiency. Real systems require more input power to deliver the calculated output. Apply an efficiency factor to get the true input requirement.
• Using weight in kg instead of force in N: The force field requires newtons. To convert a mass in kg to a gravitational force, multiply by 9.81. A 50 kg load exerts about 490.5 N downward.

1. 1Select the calculation method: energy/time or force × velocity.
2. 2For energy/time: enter energy in joules and time in seconds. The calculator divides them to get power in watts.
3. 3For force/velocity: enter force in newtons and velocity in metres per second. The calculator multiplies them.
4. 4Power in watts is converted to kilowatts (divide by 1000) and horsepower (divide by 745.7).
5. 5The energy-in-1-minute figure (force-velocity mode) shows how much energy the system delivers each minute.
6. 6All inputs must be positive; the calculator returns an error otherwise.

• Convert kW to hp by multiplying by 1.341: A quick way to compare metric and imperial power ratings: 1 kW = 1.341 hp. A 100 kW engine is approximately 134 hp.
• Use the force-velocity method for constant-speed scenarios: For an object moving at steady speed (no acceleration), the driving force equals drag or friction. Multiply that force by speed to get the power required to maintain that speed.
• Relate power to energy bills: Electricity is billed in kWh. Power in kW × hours of operation = energy in kWh. A 2 kW heater running 5 hours uses 10 kWh. At $0.20/kWh, that costs $2.00.
• Peak vs. continuous power ratings: Motor and engine specs often list peak power alongside continuous (rated) power. Use the continuous figure for sustained load calculations; peak applies only to short bursts.