Enter the power value in watts into the calculator to determine the milliwatt value; this calculator can also evaluate the power value given the milliwatt value is known.

Milliwatt Formula

The following formula is used to calculate the milliwatt (mW) value:

mW = P * 1000


  • mW is the milliwatt value
  • P is the power value in watts

To calculate the milliwatt value, multiply the power value in watts by 1000.

What is a Milliwatt?

A milliwatt is a unit of power that is equal to one thousandth (1/1000) of a watt, which is the standard unit of power in the International System of Units (SI). It is commonly used in telecommunications, electronics, and physics to measure small amounts of power, such as the power output of a transmitter or the power consumption of a small electronic device. The term milliwatt is derived from the word ‘milli’, a prefix in the metric system denoting a factor of one thousandth, and ‘watt’, a unit of power named after James Watt, a Scottish engineer and inventor. The symbol for milliwatt is ‘mW’. For example, a typical laser pointer might have a power level of 5 milliwatts, while a typical smartphone might consume around 500 milliwatts of power during use.

How to Calculate Milliwatt?

The following steps outline how to calculate the Milliwatt:

  1. First, determine the power output (mW).
  2. Next, determine the time taken (s).
  3. Next, gather the formula from above = Milliwatt = Power Output / Time Taken.
  4. Finally, calculate the Milliwatt.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Power Output (mW) = 120

Time Taken (s) = 5