Power Calculator (Physics)
Energy Tells You How Much; Power Tells You How Fast
Two engines can do the exact same amount of work and still be rated completely differently, because power measures the rate at which that work gets done, not the total amount. A weaker engine can move the same load as a stronger one — it just takes longer. This calculator solves power two ways: from energy delivered over time, or from force and velocity for something already in steady motion.
The Formulas
From force and velocity: P = F × v
Both forms describe the same underlying quantity, measured in watts (joules per second). The energy-time form suits anything with a defined start and finish; the force-velocity form is more natural for continuous motion, like a vehicle cruising at constant speed against resistance.
Where Power Ratings Actually Decide Outcomes
- Engine and motor specification — horsepower and wattage ratings tell you how quickly a machine can do work, which determines acceleration, climbing ability, and throughput.
- Electrical system design — wiring, breakers, and batteries are sized around power draw (watts), not just total energy consumption.
- Human performance — cycling and rowing training is frequently measured directly in watts, since sustained power output is a strong predictor of athletic performance.
- Renewable energy systems — solar panels and wind turbines are rated by peak power output, a critical spec for matching generation to demand.
Typical Power Output, for Scale
| Source | Typical Power |
|---|---|
| Resting human metabolism | ~100 W |
| Trained cyclist, sustained effort | ~250–300 W |
| Household incandescent bulb | 60 W |
| Typical passenger car engine | ~100,000–150,000 W (roughly 130–200 hp) |
Widely cited approximate reference figures; actual values vary by individual, appliance model, and vehicle.
How to Use This Calculator
- Choose a mode: From Energy and Time or From Force and Velocity.
- For the energy-time mode, enter Energy/Work (J) and Time (s).
- For the force-velocity mode, enter Force (N) and Velocity (m/s).
- Select Calculate to get power in watts along with the worked formula.
Related Calculations
To see the work being done before dividing by time, use the Work Calculator, or find the force behind a given mass and acceleration with the Force Calculator.