Which is equal to 500 milliwatts?

The metric prefix 'milli-' stands for one one-thousandth. This means it takes 1,000 milliwatts to equal a single watt. To convert from milliwatts to base watts, you must divide the value by 1,000. You can easily do this by moving the decimal point three places to the left. Dividing 500 by 1,000 yields exactly 0.5 watts. Distractors like 5 or 50 watts occur if you move the decimal point the wrong number of places or confuse 'milli' with another prefix like 'centi' or 'deci'.