physics

Power Calculator (Physics)

Calculate power (rate of doing work) from work and time, or from force and velocity. Essential for mechanics, engines, and energy.

Reviewed by Christopher FloiedUpdated April 16, 2026

This free online power calculator (physics) provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

Work Done (Joules)

Time (seconds)

How to Use This Calculator

Enter your input values

Fill in all required input fields for the Power Calculator (Physics). Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

Read the results

The Power Calculator (Physics) instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

Formula Reference

Power Calculator (Physics) Formula

See calculator inputs for the governing equation

Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.

When to Use This Calculator

•Use the Power Calculator (Physics) when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
•Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
•Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
•Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

About This Calculator

The Power Calculator (Physics) is a free, browser-based calculation tool for engineers, students, and technical professionals. Calculate power (rate of doing work) from work and time, or from force and velocity. Essential for mechanics, engines, and energy. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.

About Power Calculator (Physics)

The Power Calculator computes the rate at which work is done or energy is transferred. Power is one of the most important concepts in physics and engineering — it quantifies how quickly energy flows between systems. While two machines might do the same total work, the one that does it faster has more power. This distinction matters enormously: a strong person and a weak person can both eventually lift a heavy weight onto a shelf, but only the strong person does it with high power. Power is measured in watts (W), named after James Watt, whose steam engine improvements sparked the Industrial Revolution. Whether you're analyzing electric motors, calculating workout intensity, designing heating systems, or evaluating vehicle performance, understanding power is essential.

The Math Behind It

Power is the rate at which work is done or energy is transferred. It's measured in watts (W), where 1 watt = 1 joule per second. **The Formulas**: **From work and time**: P = W / t **From force and velocity**: P = F × v Where: - P = Power (watts) - W = Work (joules) - t = Time (seconds) - F = Force (newtons) - v = Velocity (m/s) **Units**: - **SI**: Watt (W) = J/s = kg·m²/s³ - **Imperial**: Horsepower (hp), foot-pound per second - **1 hp** = 745.7 watts - **1 kW** = 1000 W - **1 MW** = 1,000,000 W **Common Power Values**: | Object | Power | |--------|-------| | LED light bulb | 5-20 W | | Incandescent bulb | 40-100 W | | Human (sitting) | ~100 W | | Human (walking) | ~250 W | | Human (intense exercise) | 500-1000 W | | Elite cyclist (peak) | 2000 W+ | | Refrigerator | 150-500 W | | Microwave | 600-1200 W | | Electric heater | 1000-1500 W | | Toaster | 800-1500 W | | Water heater | 3000-5500 W | | Air conditioner | 500-3000 W | | Tesla Model S | 500 kW (670 hp) | | Average home | 1-2 kW avg, 10 kW peak | | Wind turbine | 2-5 MW | | Nuclear reactor | 1000 MW | | Sun's output | 3.8 × 10²⁶ W | **Watts and Horsepower**: James Watt coined the term 'horsepower' in the 1780s to compare his steam engines to the horses they were replacing. He calculated that a typical horse could do about 746 watts of work sustained over time. Conversion: 1 hp = 745.7 W Most countries use kilowatts (kW) now except in automotive contexts where horsepower persists culturally. **Energy vs Power**: - **Energy**: How much work total (joules) - **Power**: Rate of doing work (watts) Analogy: - **Water energy**: Total water in a tank - **Water power**: Rate of water flow You can use LOTS of power for a SHORT time (weightlifter), or LITTLE power for a LONG time (marathoner). Both consume energy. **Kilowatt-Hour (kWh)**: The energy unit used in electric bills: 1 kWh = 1 kW × 1 hour = 3,600,000 J = 3.6 MJ You're billed for ENERGY (kWh) not POWER (kW), though peak power matters for infrastructure. **Example**: - 100W light bulb running for 10 hours = 1 kWh - 1500W heater running for 2 hours = 3 kWh - Monthly home usage: typically 500-1500 kWh **Calculating Power Examples**: **Climbing Stairs**: 70 kg person climbing 5 m in 10 seconds Work = mgh = 70 × 9.81 × 5 = 3433.5 J Power = 3433.5 / 10 = 343.35 W **Lifting Weights**: Lifting 100 kg barbell 0.5 m in 1 second Work = 100 × 9.81 × 0.5 = 490.5 J Power = 490.5 / 1 = 490.5 W (650 hp!) **Running**: Running 100 m in 12 seconds using ~8000 J of energy Power ≈ 8000/12 = 667 W **Power in Circuits**: For electrical circuits: P = V × I (power = voltage × current) P = I² × R (resistance form) P = V² / R (alternative form) Examples: - 120V × 5A = 600 W (US outlet running an appliance) - 12V battery × 2A = 24 W (car accessory) **Human Power Output**: | Activity | Power | |----------|-------| | Basal metabolism | 70-100 W | | Walking | 200-300 W | | Jogging | 400-600 W | | Fast running | 700-1000 W | | Sprinting | 1000-2000 W | | Elite sprinter peak | 2500+ W | | Weightlifter (brief) | 3000-4000 W | Note: Power is brief peaks for intense activities. Sustained power is much lower due to fatigue. **Average vs Peak Power**: - **Peak power**: Maximum instantaneous rate - **Average power**: Total energy / total time A sprinter can peak at 2500 W but average only 800 W over a 400m race. For sustained effort, lower averages. **Horsepower in Cars**: Modern vehicle power: - Compact car: 100-150 hp (75-112 kW) - Mid-size sedan: 150-250 hp - Sports car: 300-500 hp - Supercars: 500-1000+ hp - Tesla Model S Plaid: 1020 hp - Bugatti Chiron: 1500 hp - Electric Formula 1: 680+ hp (peak) - NASCAR: 750 hp **Efficiency**: Real machines aren't 100% efficient. Power output < power input: Efficiency = Power out / Power in - Incandescent bulb: ~5% (95% wasted as heat) - LED: 20-30% - Internal combustion engine: 20-30% - Electric motor: 85-95% - Hydroelectric: 80-90% - Solar panel: 20-25% **Power and Energy Conservation**: Energy can't be created or destroyed, so power is a flow: - Electric power plant: Chemical/nuclear/kinetic → Electrical - LED bulb: Electrical → Light (+heat) - Motor: Electrical → Mechanical - Battery: Chemical → Electrical Each step has efficiency losses. **Why It Matters**: 1. **Engineering**: Motors, engines, electronics all rated in power 2. **Energy use**: Bills, capacity planning 3. **Biology**: Metabolism, exercise science 4. **Sports**: Training intensity 5. **Technology**: Computer CPUs, LEDs, batteries 6. **Environment**: Power plant output **Interesting Comparisons**: - Sun's output: 3.8 × 10²⁶ W (almost unimaginable) - Earth receives: ~173,000 TW from sun - Earth's total energy use: ~18 TW - Sun provides ~10,000× our needs - 1 square meter of sunlight: ~1,000 W (at noon) **Common Mistakes**: 1. **Confusing power and energy**: Power is the RATE 2. **Unit conversions**: W vs kW vs hp vs BTU/hr 3. **Peak vs average**: Cars list peak HP; daily driving uses much less 4. **Ignoring efficiency**: Output power < input power 5. **kWh confusion**: It's energy (W × time), not power

Formula Reference

Power from Work

P = W / t

Variables: W = work (J), t = time (s)

Power from Force/Velocity

P = F × v

Variables: F = force (N), v = velocity (m/s)

Unit

1 watt = 1 joule/second

Variables: SI unit of power

Worked Examples

Example 1: Worker Lifting Crates

Worker lifts 500 J of crates in 5 seconds.

Step 1:P = W / t

Step 2:P = 500 / 5

Step 3:P = 100 W

Power: 100 watts. About the same as an incandescent light bulb. This is a sustainable rate for manual labor over hours.

Example 2: Sprinter Peak Power

Sprinter applies 800 N force while running at 12 m/s at peak speed.

Step 1:P = F × v

Step 2:P = 800 × 12

Step 3:P = 9,600 W

Peak power: 9,600 watts (~13 horsepower!). This is brief — sprinters sustain it for just a few seconds at maximum. Usain Bolt's peak during his world record was approximately 2,600 W at 12.4 m/s.

Common Mistakes & Tips

!Confusing power with energy. Power is the rate; energy is the total amount.
!Mixing units. Watts, kW, hp, BTU/hr all measure power but differ by factors.
!Using peak power for averages. Devices rarely operate at maximum continuously.
!Ignoring efficiency. Input power is always more than output due to losses.

Related Concepts

Work Calculator

Calculate work done by force.

Kinetic Energy

Energy of motion.

Potential Energy

Stored energy.

Used in These Calculators

Calculators that build on or apply the concepts from this page:

Ohm's Law Calculator

Frequently Asked Questions

What's the difference between power and energy?

Energy is TOTAL work done or heat transferred (measured in joules). Power is the RATE at which energy is used (measured in watts = J/s). A light bulb has a power rating (100 W), and running it for an hour uses 100 Wh or 360,000 J of energy. Power is like speed; energy is like distance.

Why does my electric bill show kWh, not watts?

Your electric bill charges you for ENERGY consumed, not power. Power is the rate (watts), energy is the total (watt-hours). A 1000W heater running 1 hour = 1 kWh. A 100W bulb running 10 hours = also 1 kWh. They cost the same to run. Your utility company charges roughly $0.10-0.30 per kWh.

Is horsepower the same as watts?

They measure the same thing (power) but in different units. 1 horsepower = 746 watts. To convert: multiply hp by 746 to get watts, or divide watts by 746 to get hp. A 200 hp car has ~149 kW power output. Horsepower is cultural/automotive; watts are scientific/engineering standard.

How much power does a human produce?

Varies enormously. Resting: ~100 W (like an old light bulb). Walking: ~200-300 W. Jogging: 400-600 W. Sprinting: 1000-2500 W briefly. Elite cyclists sustain 300-400 W for hours. Peak anaerobic efforts reach 3000-5000 W briefly. The human body is remarkable for its power-to-weight ratio, especially compared to machines with similar mass.