What is Watt

Watt is a basic unit of all types of power like electrical power, mechanical power or thermal power.

Watt is named after the scientist James Watt, who invented Steam engine. He is a Scottish scientist lived in the period of 1736- 1819. He improved steam engine and contributed greatly to the usage of steam power in our day to day life. In memory of his contribution International System of Units have coined the term Watt which is used for measurement of Power.


  • Watt is defined as the rate at which the energy is converted, generated or transferred with respect to time.
  • Watt is also defined as the rate at which the  work is done and expressed as Joules per second
  • The formula for Watt is
    • W = J / S

Where W stands for Watts, J stands for Joules, S stands for a second.

  • 1 W = 1.341 X 10-3 HP

HP stands for Horsepower.

  • Watt is the SI (International system of units) unit of Power.
  • The symbol or abbreviation of Watt is W.

Electrical Watt:

  • The electrical unit of Watt can be defined as one ampere current flow in one volt.
    • W = A x V  or
    • P = A x V

Where A stands for Ampere, V stands for Volt, P stands for Power generated.

  • So it is easy to calculate Watt for any of the electrical systems we use. The power generated by the electrical device can be calculated by knowing two important values and by multiplying them. They are
    • Current which is expressed in Ampere
    • The voltage which is expressed in Volt.
  • Current as Ampere, Volt as Voltage and Power as Watts are the three terms which are used to describe electricity.
  • We use this formula to calculate the power generated in Direct current ( DC ) systems and also in Alternating Current (AC) systems
  • In terms of Electrical Energy Watt is nothing but the power which is used to transfer of energy
  • Whereas in terms of electromagnetic energy, Watt is a unit which is used to absorb the radiation or reflect the radiation or transmit the radiation.
  • In circuits like RF circuits which is also called as radio frequency circuits, the calculation of power will be more complex because it is not the resistance which determines the power generated or utilized but it is the reaction of the radiation which determines the power transferred. Because the radiation energy is more absorbed, reflected or radiated. Here the energy will be dispersed or radiated and can be measured by a special instrument called RF watt meter.

Units of Watt: –

There are various quantities of Watt used and they are as follows:

  1. 1 Kilowatt is equal to   1000 W
  2. 1 megawatt is equal to 1000,000 W (10 6 )
  3. 1 gigawatt is equal to 1000,000,000 W ( 10 9 )
  4. 1 terawatt is equal to 1000,000,000,000 W ( 10 12 )
  5. 1 petawatt is equal to 1000,000,000,000,000W ( 10 15 )

All these values are positive values of Watts whereas negative values of Watt are as follows

  • 1 Milliwatt is equal to 1 / 1000 Watt
  • 1 nanowatt is equal to 10-9
  • 1 microwatt is equal to 10-6 watt
  • 1 picowatt is equal to 10-12 Watt
  • 1 HP (Horsepower) is equal to 746 Watts.

Applications of Watt:-

  • Nano watts are used in Radar and radio devices
  • Medical investigations like Electrocardiogram (ECG) and Electroencephalogram (EEG) uses microwatts as their units in their investigation.
  • Medical devices like hearing aid use less than one Millie-watts whereas Lasers used for eye surgery, dental surgery and other applications use Millie-watt.
  • Picowatt (pW) are used in various radio and radar receivers and they are also used in astronomical studies
  • Kilowatt has various applications. The unit Kilowatt is used in many electrical power generators like AC and heaters.
  • One common example of Watt is our electrical bulb. The power of electrical bulb is represented by Watts.
  • Gigawatt is a unit used in many power plants where electricity is generated.
  • Some of the lasers which are powerful, use either Terawatt or petawatt.
  • The whole human power is expressed in Terawatt.
  • A megawatt is used in industries of power production.
  • It is a unit used to describe the power of many of our normal household appliances like refrigerators, microwave ovens, washing machines etc.

Ohm’s Law: –

Ohm’s law is otherwise called as Watts’s law. Ohms law is defined as the voltage across the circuit is directly proportional to the current flowing and the resistance of the circuit. It is also defined as current flow through a conductor is directly proportional to the voltage and inversely proportional to the resistance of the conductor

V = I X R

Where V is the Volt, I is the current, R is the resistance.

We already know that Watt is the multiple of voltage and current.

W         = V X I

W          = (I X R) x I

by substituting the values of Voltage (V)

= I x R

Where W is the power.

  1. Watt is the power of an electronic device measured with the use of current flowing through them and the voltage
  2. Whereas Watt per hour is the power generated at a particular time like one hour of an electronic device.
  3. So watt and Watt-hour are the commonly confused terms and should be clearly understood.
  4. Briefly, we can say that Watt is a measure of Power while Watt Hour is a term used to describe energy.

Watt Meter: –

Watt meter is an instrument used to measure the power or electrical energy and it is expressed in Kilowatt- hour.