How to Calculate an RMS

RMS is often used in electrical engineering.
••• calculator image by Szymon Apanowicz from Fotolia.com

The Root Mean Square, or quadratic mean, is a statistical function for finding the average of a series even if it contains negative numbers. When you have a series with negative numbers, the normal formula for averaging -- adding all the numbers and dividing by the number of numbers -- will give you the "middle value," but it won't give you a sense of the average magnitude. RMS tells you how big the average number is, no matter which side of the number line it's on. Most real-world RMS problems must use calculus, but you can find the RMS of a small series with basic math and a calculator.

    Count the number of numerals you are finding the RMS for. For example, if you have the series 5, -3 and -7, you have three numerals.

    Square each of the numbers, either in your head or with a calculator. Write each one down on a piece of paper as you go so you don't lose track of them. For example, the squares of 5, -3 and -7 are 25, 9 and 49.

    Add all the squares together. For our series, 25 + 9 + 49 = 83.

    Divide the sum of the squares by the number of numbers. 83 divided by 3 is 27.67.

    Take the square root of the sum divided by the number of numbers. The square root of 27.67 is 5.26, so for the series 5, -3 and -7, the RMS is 5.26.

Related Articles

How to Find the Average of Integers
Definition of Mean, Median & Mode
What is the First Quartile?
How to Calculate Standard Error of The Mean
How to Calculate With the Taylor Series
Definition of Successor and Predecessor in Math
How to Find the Common Ratio of a Fraction
How to Calculate Arctan
How do I Calculate the Geometric Mean on an HP 12C?
How to Calculate the Geometric Mean
How to Calculate Statistical Mean
How to Calculate Logarithmic Mean
Difference Between the Mean & the Average
How to Calculate SSE
Explain the Mean, Mode & Median
How to Calculate Dispersion
How to Calculate Mean Deviation
Define Mean for Math
How to Calculate Millivolts to Amps

Dont Go!

We Have More Great Sciencing Articles!