Power conversion

What is a power calculator used for?

In various fields of engineering, different power units are used – this applies to both the SI system (watts or joules per second) and engineering practice (e.g., horsepower or volt-amperes). Our calculator allows for quick and precise conversion of the most commonly used power units, facilitating data analysis and the selection of appropriate components.

When is it worth using the calculator?

• When comparing specifications of power supplies, inverters, and receivers;
• When selecting electrical devices based on active and apparent power;
• During the conversion of horsepower to kilowatts in drive systems;
• In working with documentation that specifies power in ergs or joules per second.

Table of power units used in the calculator

The table below presents the units available in the calculator and their relation to the watt – the basic unit of power in the SI system. Unit Symbol Value in watts Typical application Milliwatt mW 0.001 low power systems, signals, precision electronics Watt W 1 basic power unit, electronics, power supply Kilowatt kW 1000 household and industrial devices, engines Megawatt MW 1,000,000 power engineering, high power installations Horsepower HP 735.5 automotive, mechanical drives (metric system) Joule per second J/s 1 physics, science, power as energy flow Erg per second erg/s 1.00E-07 microscales, scientific applications, classical physics Volt-ampere VA ≈1 (at cosφ=1) apparent power in AC circuits

How does the power unit conversion work?

Simply enter the value, select the input and target unit. The calculator uses accurate conversion coefficients. This allows you to:

• convert milliwatts to watts or kilowatts,
• compare mechanical power in HP with electrical power in kW,
• check the equivalence of VA and W in an ideal system,
• convert joules per second or erg/s to practical units.

All without the need to look up converters manually.

Practical applications of the power calculator

The calculator can be useful in many areas:

• Selecting a power supply for an electronic system with accuracy to mW;
• Comparing engines listed in horsepower and kilowatts;
• Assessing apparent power (kVA) in distribution boards or emergency power systems;
• Analyzing scientific documentation with units J/s or erg/s.

It is also a helpful tool when configuring power systems in automation, robotics, or during laboratory tests.

FAQ - Frequently Asked Questions about Power Conversion

What is the difference between a watt and a volt-ampere?

A watt (W) is a unit of active power, i.e., the actual energy consumed by a device. Meanwhile, a volt-ampere (VA) is apparent power, which includes both real and "reactive" power, occurring with phase shift.

Are kilowatts and kilovolt-amperes the same?

Not always. 1kW = 1kVA only when cos φ = 1 (full phase voltage and current alignment). Otherwise: kW = kVA × cos φ

Where is erg per second used?

Erg per second is a power unit in the centimeter-gram-second (CGS) system, representing energy (erg) over time (seconds). Erg per second is used in classical physics, including in the description of thermal, optical, or mechanical processes at microscales.

Is joule per second the same as watt?

Yes, 1J/s = 1W. This is the formal definition of a watt as energy flow over time.

Why are watts specified in power supplies and VA in transformers?

Power supplies specify active power (W), i.e., the actual power that the device delivers to the receiver. Meanwhile, transformers and UPSs often specify apparent power (VA), as they must handle both active and reactive power.

Can power be negative?

Not in the physical sense. However, in some applications (e.g., bidirectional measurements), a negative value may indicate that energy is being returned, not consumed, e.g., in energy recovery systems (regeneration).

Did you know...

• The famous unit of horsepower (HP) was introduced by James Watt, who wanted to compare the efficiency of a steam engine to the pulling power of a horse. Based on the power of a horse pulling a water mill, Watt calculated that an average horse could perform work of 550 pounds per second over a distance of 1 foot, which today translates to 735.5W (in the metric version). Thus, the power of 1 horsepower is about 735W, but in the USA, a value of 746W is accepted.
• The sun emits about 3.8 × 10²⁶ watts of power, equivalent to the power of 10²³ nuclear power plants operating simultaneously.
• An average person at rest produces about 100W of power, the same as a classic light bulb. During intense effort (e.g., sprinting, weightlifting): up to 700–1000W. Professional cyclists in the Tour de France race can generate an average of 300–400W for several hours.
• 1 megawatt (MW) is enough power to supply even 1000 standard single-family homes.
• Decibel (dB) is not an SI unit, but is indispensable in audio, communication, and RF electronics. It is derived from Alexander Graham Bell. It is used to compare power and voltages on a logarithmic scale to facilitate working with large ranges.
• 1mW = 0.001W – enough to power an LED indicator or a Bluetooth transmitter in energy-saving mode. In IoT systems, consumption is often aimed to be below 10mW to extend battery life to several years.
• 1MW is a power unit used in designing power plants, large industrial facilities, and data centers. A typical new-generation wind turbine produces 3–5MW of peak power, and the largest power plants (e.g., nuclear) achieve even 5000–6000MW (5–6GW).
• Although erg is an "archaic" unit (1erg = 1e-7J), it still appears, for example, in plasma physics, astronomy, and spectroscopy. In the 1960s, physicists used erg/s in descriptions of star radiation. This is an example of how diverse units can be even in today's science.