What does RMS stand for?

• A. Root Mean Square
• B. Root of the mean of the squares
• C. root of the mean of the squares
• D. Square root of the mean squares

Answer: (B)

RMS stands for Root Mean Square. It’s the square root of the average of the squares of a set of numbers. You square each value to make all contributions positive, average those squared values to get the mean of the squares, and then take the square root to return to the original units. This measure is handy for comparing magnitudes of fluctuating quantities, like AC voltages or currents, because it reflects the amount of power they would deliver if they were DC with the same heating effect. The description “root of the mean of the squares” describes the same calculation, but the standard name used is Root Mean Square.