# Microsoft Office Application Help - Excel Help forum > Excel Formulas & Functions >  > [SOLVED] Root mean square (RMS) error formula

## Lea Olsen

Hello,

does anyone know what the formula for calculating root mean square (RMS)
error is? Can this be done in Excel?

Thanks,

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## John Mansfield

Lea,

This web site looks like it might have the Excel calculation that you're
looking for:

http://geology.asu.edu/~glg410/2000/...ingSolver.html

----
Regards,
John Mansfield
http://www.pdbook.com

"Lea Olsen" wrote:

> Hello,
>
> does anyone know what the formula for calculating root mean square (RMS)
> error is? Can this be done in Excel?
>
> Thanks,
>
>

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## Harlan Grove

"Lea Olsen" <Lea Olsen@discussions.microsoft.com> wrote...
>does anyone know what the formula for calculating root mean square (RMS)
>error is? Can this be done in Excel?

RMS is just the (population) standard deviation of your residuals. If you
have actual data, Y, and fitted estimates of those data points, Z, your RMS
is given by the array formulas

=SQRT(DEVSQ(Y-Z)/COUNT(Y))

or

=STDEVP(Y-Z)

The former is less susceptible to truncation error.

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