Enter values to see results
—
W
—
kW
—
hp
Enter values to see results
—
W
—
kW
—
hp
Power is the rate at which work is done or energy is transferred. While work tells you the total energy involved, power tells you how quickly that energy is delivered. A powerful engine and a weak motor can both do the same total work, but the powerful engine does it in less time. The SI unit of power is the watt (W), where 1 W = 1 J/s.
This Power Calculator supports two common formulations: $$P = \frac{W}{t}$$ (work divided by time) and $$P = F \cdot v$$ (force times velocity). The first is useful when you know the total energy transferred and the duration. The second applies to situations where a constant force drives an object at steady velocity — such as a car maintaining speed against drag or a motor lifting a load at constant rate. Results are provided in watts, kilowatts, and horsepower for broad applicability across physics, engineering, and everyday contexts.
The two power formulas are:
$$P = \frac{W}{t}$$ — average power equals work done divided by time taken.
$$P = F \cdot v$$ — instantaneous power equals the product of force and velocity (when force is parallel to velocity).
The second form is derived from the first: since $$W = Fd$$ for constant force and $$v = d/t$$, we get $$P = Fd/t = Fv$$. The watt is named after James Watt, who also popularized the horsepower unit (1 hp = 745.7 W). A kilowatt (kW) equals 1000 W and is commonly used for electrical appliances and vehicle engines.
A 60 W light bulb converts 60 joules of electrical energy per second. A human can sustain about 75 W (0.1 hp) of mechanical power output during activities like cycling. A typical car engine produces 100–300 hp (75–224 kW). The power value helps you determine time requirements: to do 10,000 J of work at 500 W takes 20 seconds.
Inputs
Results
Lifting 100 kg by 5 m (W = 100×9.81×5 = 4905 J) in 3 seconds requires P = 4905/3 = 1635 W (2.19 hp).
Inputs
Results
A car overcoming 800 N of drag at 30 m/s (108 km/h) needs P = 800 × 30 = 24,000 W (32.2 hp).
Energy (joules) is the total capacity to do work, while power (watts) is the rate of energy transfer. Energy = Power × Time. A 100 W bulb running for 1 hour uses 100 × 3600 = 360,000 J = 0.1 kWh of energy.
Both measure power. 1 mechanical horsepower = 745.7 watts. Horsepower was defined by James Watt as the power a draft horse could sustain. The watt is the SI standard used in science and most of the world.
Yes. Negative power means energy is being extracted from a system. For example, regenerative braking in electric vehicles produces negative power — the motor acts as a generator, converting kinetic energy back to electrical energy.
A healthy adult can sustain about 75 W (0.1 hp) of mechanical power for extended periods (e.g., cycling). During short bursts (sprinting, jumping), peak power can reach 1,000–2,000 W. Elite cyclists sustain 300–400 W for an hour.
Use $$P = Fv$$ when you know the instantaneous force and velocity, especially for steady-state problems (constant speed against friction). Use $$P = W/t$$ when you know the total work and total time. Both give the same result for constant force and velocity.
In electrical circuits, power is $$P = VI$$ (voltage × current), $$P = I^2R$$, or $$P = V^2/R$$. These are analogous to the mechanical formulas, with voltage playing the role of force and current the role of velocity.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
How helpful was this calculator?
Be the first to rate!
Work Calculator
Work, Energy & Power Calculators
Kinetic Energy Calculator
Work, Energy & Power Calculators
Potential Energy Calculator
Work, Energy & Power Calculators
Elastic Potential Energy Calculator
Work, Energy & Power Calculators
Work and Power Calculator
Work, Energy & Power Calculators
Mechanical Advantage Calculator
Work, Energy & Power Calculators
