# How to Calculate an RMS

Save

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.

### Things You'll Need

• 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.

## References

• Photo Credit calculator image by Szymon Apanowicz from Fotolia.com
Promoted By Zergnet

### You May Also Like

• How to Calculate RMS Value

Technically, the root mean square (RMS) of a variable is the square root of the average of the square of the variable....

• How to Calculate RMS Watts

Alternating current (AC) rises and falls following a sinusoidal rhythm, making it difficult to describe average values associated with AC electrical circuits....

• How to Calculate RMS Wattage for a Car Amplifier

Anyone who has purchased an amplifier or set of speakers has seen an "RMS wattage" figure printed on the outside of the...

• How to Calculate the RMSE or Root Mean Squared Error

When you graph several scientific data points, you may wish to fit a best-fit curve to your points, using software. However, the...

• How to Calculate RMSD

If you've ever used a graphing calculator for advanced mathematical problems, chances are you've used a Texas Instruments calculator. ... Root mean...

• How to Calculate IRMS

The current in an alternating current circuit varies continuously in direction and magnitude. Calculations involving the current don't therefore consider the current...

• How to Calculate the Root MSE in ANOVA

How to Calculate the Root MSE in ANOVA. In statistics, the analysis of variance (ANOVA) ... How to Calculate RMSD. The root...

• How to Calculate Mean Squares Within

How to Calculate Mean Squares Within. ... How to Calculate an RMS. Root mean square (RMS) is a calculation used by mathematicians...

• How to Convert AC Voltage to DC

Calculate the "peak" voltage output by multiplying the given "rms" (root mean square) ... The rms voltage is the "effective" value of...

• What Does RMS Stand for in Speakers?

Root Mean Squared, or RMS, is a formula used to calculate an approximate average for the power an amplifier can continuously create...