Power Converter

Power is the rate at which energy is used, transferred, or converted, and depending on the industry, it’s measured in different units. Electrical systems commonly use watts or kilowatts, while mechanical setups often rely on horsepower. To avoid manual math and reduce costly errors, a power conversion calculator makes switching between these units quick and reliable.

Whether you're designing an electrical circuit, running heavy equipment, or calculating your home’s energy usage, having a precise power conversion method ensures your work is both efficient and accurate.

Power Units and Conversion

Power is a universal concept across fields like engineering, mechanics, thermodynamics, and even cosmology. Here's a breakdown of the most widely used power units and where they’re applied:

SI (Metric) Units

• Watt (W) – The fundamental SI unit of power, defined as one joule per second.
• Milliwatt (mW) – 1/1,000th of a watt, used for low-power devices like lasers and small electronics.
• Kilowatt (kW) – Equal to 1,000 watts, commonly used for electrical appliances and industrial power.
• Megawatt (MW) – Equal to 1,000 kilowatts, used for large-scale power generation and consumption.
• Gigawatt (GW) – Equal to 1,000 megawatts, often used for national power grids and major energy production facilities.
• Terawatt (TW) – Equal to 1,000 gigawatts, used for measuring global energy consumption.

Mechanical and Thermal Power Units

• Horsepower (hp) – A traditional unit of power used in engines and machinery. One mechanical horsepower is approximately 745.7 W.
• Metric Horsepower (hpₘ) – A variation of horsepower, primarily used in Europe, approximately 735.5 W.
• Electrical Horsepower (hpₑ) – Defined as 746 W, often used for electric motors.
• Boiler Horsepower (hp_b) – A unit used to measure the output of steam boilers, equal to approximately 9,810 W.
• Foot-pound per second (ft⋅lbf/s) – A mechanical unit measuring the power needed to move one pound-force over a foot in one second, approximately 1.356 W.

Thermal and Refrigeration Power Units

• British Thermal Unit per hour (BTU/h) – A common unit in HVAC, where 1 BTU/h ≈ 0.2931 W. (Since thermal power output is affected by temperature, accurate unit conversion may require a Temperature Converter as well.)
• British Thermal Unit per second (BTU/s) – Used in higher-power thermal calculations, where 1 BTU/s ≈ 1,055 W.
• Ton of Refrigeration (TR) – A unit measuring cooling power, widely used in air conditioning, where 1 TR ≈ 3.516 kW. (Cooling and heating systems often rely on fluid volumes — convert between gallons, liters, and more using our Volume Converter.)

Cosmic and Theoretical Units

• Planck Power – A theoretical unit of power in physics, equal to 3.628 × 10⁵² W, used in cosmology and quantum mechanics.

James Watt: The Man Behind the Watt

The watt (W)—our modern unit of power—is named in honor of James Watt, a Scottish engineer whose ideas helped reshape the industrial world. Born in 1736, Watt made a major leap in 1763 when he was called on to fix a Newcomen steam engine. While repairing it, he realized the machine was highly inefficient, so he invented the separate condenser, a change that drastically boosted steam engine performance. This innovation played a huge role in powering the Industrial Revolution, driving progress in factories, locomotives, and ships.

To explain the strength of his engines, Watt came up with the idea of horsepower (hp)—a relatable way to communicate power output. Later, as electricity became more common, the watt was officially adopted as the standard unit of power. Watt’s contributions didn’t just change how machines ran—they laid the foundation for how we measure and understand energy today. Whether you're looking at a light bulb or a massive power plant, each watt in use reflects James Watt’s enduring influence on engineering and energy systems.

A watt is defined as one joule per second (J/s), meaning it represents the amount of energy used or produced per unit time.

Mathematically, it can be expressed as:

1 W = 1 J/s

Where:

• J (joule) is a unit of energy
• s (second) is the time over which the energy is transferred

Since power and energy often go hand in hand, our Energy Converter is useful for switching between joules, calories, or kilowatt-hours depending on your context.

Watt in Electrical Power

In the context of electricity, power is calculated as the product of current (amperes, A) and voltage (volts, V):

1 W = 1 A × 1 V

Where:

• A (ampere) measures electric current
• V (volt) measures electrical potential difference

Curious how power usage affects your electricity bill? Try our Electricity Cost Calculator to estimate daily or monthly consumption in watts and kilowatt-hours.

SI Multiples for Watt (W)

The watt (W) is often used with different prefixes to represent power levels that vary from incredibly tiny to massively large. Thanks to the International System of Units (SI), we can easily scale these values using standardized prefixes—making it much simpler to communicate power across scientific, industrial, and technological contexts.

The following table breaks down the most common SI multiples of the watt, along with their symbols and where you might typically encounter them in real-world applications:

When working across different units of power or energy, using our Conversion Tools ensures quick and accurate calculations—especially helpful when converting watts to kilowatts or megawatts.