Power from work, force and velocity, or voltage and current
Power is the rate at which work is done or energy is transferred. Average power equals work divided by elapsed time when the work and time interval are known.
Instantaneous mechanical power is the dot product of force and velocity, so the calculator requires the force component parallel to motion. In a direct-current electrical relationship, power equals voltage multiplied by current.
How to use the power calculator
- Choose a relationship: Select general, mechanical, or electrical power.
- Select the unknown: Choose the variable to calculate.
- Enter values and units: Supply the other two quantities using the available units.
- Calculate: Generate the result and review the formula shown below it.
Formula and variables
Choose the relationship matching the physical system, then solve for any one of its three variables.
P = W/t; P = F∥v; P = VI- P — Power
- Rate of work or energy transfer (W)
- W — Work
- Energy transferred over an interval (J)
- F∥ — Parallel force component
- Force component along velocity (N)
- V, I — Voltage and current
- Electrical potential difference and current (V, A)
Mechanical power from force and speed
A 200 N force component acts parallel to motion at 5 m/s.
- F∥
- 200 N
- v
- 5 m/s
- P = F∥v
- P = 200 × 5 = 1,000 W
Result: The mechanical power is 1,000 W or 1 kW.
Only the force component parallel to velocity contributes to the dot product.
Understanding your results
Sign and direction
Mechanical and electrical power may be signed depending on the chosen direction and passive-sign conventions.
- One watt equals one joule per second.
- Mechanical horsepower in this calculator is approximately 745.6999 W.
- The electrical mode uses P = VI and does not add power-factor or AC phase corrections.
Assumptions
- Average power is represented by constant work divided by elapsed time.
- Mechanical force is the component parallel to velocity.
- Electrical voltage and current values are compatible with the simple P = VI relationship.
Limitations
- Does not calculate AC real, reactive, or apparent power or power factor.
- Does not resolve a force vector or angle into its parallel component.
- Does not model time-varying power by integration.
Common mistakes
- Using total force when only a component is parallel to motion.
- Mixing hours and seconds without unit conversion.
- Applying P = VI to AC values without considering phase and waveform.
- Confusing power in watts with energy in watt-hours.
Practical use cases
Work-rate problems
Calculate work, elapsed time, or average power.
Mechanical motion
Calculate signed power from parallel force and velocity.
Basic DC circuits
Calculate voltage, current, or electrical power.
Frequently asked questions
Are watts and watt-hours the same?
No. Watts measure power, while watt-hours measure energy accumulated over time.
Why does the mechanical formula use the parallel force?
Power is F·v, a dot product. A perpendicular force component contributes zero instantaneous power.
Can power be negative?
Yes. A negative sign can indicate energy is being removed from the selected system or direction convention.
Sources and review
- Power — OpenStax University Physics Volume 1. Accessed 2026-07-13.
- Electrical Energy and Power — OpenStax University Physics Volume 2. Accessed 2026-07-13.
Reviewed 2026-07-13.