Watt is the SI unit of power.
In the metric system, milli is the prefix for 10–³.
Therefore, a milliwatt (mW) is equal to one thousandth of a watt.
Formula to convert W to mW.
Since we know that a mW is equal to one thousandth of a watt.
Therefore, to convert W to mW, we multiply the watt value by 1,000.
Power in mW = Power in W x 1,000
Convert 20 Watts to milliwatts.
= 20 x 1000
= 20,000 milliwatts.