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Power Conversion Calculator

Convert between common power units: watts (W), kilowatts (kW), megawatts (MW), horsepower (hp), BTU per hour (BTU/hr), and foot-pounds per second (ft-lb/s).

Reviewed by Christopher FloiedPublished Updated

This free online power conversion calculator 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.

Minimum: 0

The numeric value to convert

Select the source power unit

Results

Watts (W)

1000 W

Kilowatts (kW)

1 kW

Megawatts (MW)

0.001 MW

Horsepower (hp)

1.341 hp

BTU/hr

3412.15 BTU/hr

How to Use This Calculator

1

Enter your input values

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

2

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.

3

Read the results

The Power Conversion Calculator 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.

4

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.

When to Use This Calculator

  • •Use the Power Conversion Calculator 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.

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About Power Conversion Calculator

The Power Conversion Calculator converts between the most common units of power used in engineering, automotive, electrical, and HVAC applications. Power measures the rate of energy transfer, with the watt (W) as the SI unit. However, horsepower remains standard for engines and motors, BTU/hr is used in heating and cooling specifications, and kilowatts and megawatts are used for electrical generation and industrial equipment. This converter normalises any input to watts and then displays all equivalent values. Whether you are comparing motor specifications, sizing HVAC equipment, or understanding power plant output, this tool provides instant cross-unit conversion.

The Math Behind It

Power is defined as energy per unit time: P = E/t. The SI unit is the watt, equal to 1 joule per second (1 W = 1 J/s). Named after James Watt, the Scottish engineer who improved the steam engine, the watt is used for electrical power (voltage times current: P = V * I), mechanical power, and thermal power. Horsepower was defined by James Watt as approximately the sustained output of a draft horse: 33,000 foot-pounds per minute or 745.7 watts. Several variants exist: mechanical (550 ft-lb/s = 745.7 W), metric (75 kgf*m/s = 735.5 W), and electrical (746 W exactly). This calculator uses mechanical horsepower. BTU per hour measures the rate of thermal energy transfer and is the standard unit for HVAC equipment ratings in the United States. Air conditioners are often rated in 'tons of cooling,' where 1 ton = 12,000 BTU/hr = 3,517 W = 3.517 kW. The relationship between power and energy is critical: energy equals power multiplied by time. A 100-watt light bulb running for 10 hours consumes 1 kWh (100 W * 10 h = 1000 Wh = 1 kWh). Electricity bills charge per kWh, not per kW. Power plant capacities are measured in megawatts (MW). A typical coal plant is 500-1000 MW, a nuclear reactor is 1000-1500 MW, and a large wind turbine is 2-5 MW. The distinction between nameplate capacity (maximum power) and average output is important; wind and solar have capacity factors of 25-45%, meaning actual output averages 25-45% of maximum. In automotive engineering, engine power in horsepower is measured at the crankshaft (brake horsepower, bhp) or at the wheels (wheel horsepower, whp). Transmission and drivetrain losses typically reduce wheel horsepower by 10-15%.

Formula Reference

Power Unit Conversions

1 kW = 1000 W, 1 MW = 10^6 W, 1 hp = 745.7 W, 1 BTU/hr = 0.29307 W

Variables: W = watt (SI unit), kW = kilowatt, MW = megawatt, hp = mechanical horsepower, BTU/hr = British thermal units per hour

Worked Examples

Example 1: Convert 1 Kilowatt to Other Units

A space heater is rated at 1 kW. Express in other power units.

Step 1:Watts: 1 * 1000 = 1000 W
Step 2:hp: 1000 / 745.7 = 1.341 hp
Step 3:BTU/hr: 1000 / 0.29307 = 3,412.1 BTU/hr
Step 4:MW: 1000 / 1,000,000 = 0.001 MW

1 kW = 1000 W = 1.341 hp = 3,412.1 BTU/hr = 0.001 MW.

Example 2: Car Engine: 200 hp to kW

A car engine produces 200 horsepower. Convert to kilowatts.

Step 1:Watts: 200 * 745.7 = 149,140 W
Step 2:kW: 149,140 / 1000 = 149.14 kW

200 hp = approximately 149.1 kW.

Example 3: HVAC System Rating

A furnace is rated at 60,000 BTU/hr. Convert to kW.

Step 1:Watts: 60,000 * 0.29307 = 17,584.2 W
Step 2:kW: 17,584.2 / 1000 = 17.58 kW

60,000 BTU/hr = approximately 17.58 kW.

Common Mistakes & Tips

  • !Confusing power (watts, rate of energy use) with energy (kilowatt-hours, total energy consumed). A 1 kW device uses 1 kWh of energy per hour.
  • !Using the wrong horsepower variant. Mechanical (745.7 W), metric (735.5 W), and electrical (746 W) horsepower differ slightly. Check which standard applies.
  • !Forgetting to distinguish between input power and output power. Motor efficiency means that electrical input power exceeds mechanical output power.

Related Concepts

Energy Conversion

Converts between energy units (joules, kWh, BTU). Energy is power integrated over time.

Efficiency

The ratio of useful output power to total input power, expressed as a percentage. No real machine achieves 100% efficiency.

Used in These Calculators

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Frequently Asked Questions

What is the difference between kW and kWh?

kW (kilowatt) is a unit of power, measuring the rate of energy use. kWh (kilowatt-hour) is a unit of energy, measuring total energy consumed. A 2 kW heater running for 3 hours uses 6 kWh.

Why do we still use horsepower?

Horsepower has been the standard engine rating since the steam age and remains deeply embedded in automotive culture and regulation. While the rest of the world increasingly uses kW, the US automotive market still primarily uses hp.

How many watts does a typical house use?

A typical US household averages about 1.2 kW of continuous power draw (roughly 900 kWh per month divided by 720 hours). Peak demand during heavy use can reach 5-10 kW.

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