Disclaimer: I do not hold a degree in mathematics (heck, I flunked college
algebra the first time around) and I don't even play one on TV or in any
Intel advertisements. But...

You got me curious so I went searching for coded solutions to the problem
and couldn't find any expressed as an Excel formula. What I did discover is
that a sharp fellow by the name of Srinivasa Ramanujan came up with 2
formulas in 1914 that are now accepted as being very accurate, with the 2nd
effort being the more accurate of the two. All this is shown at
http://en.wikipedia.org/wiki/Circumference

So I worked at implementing his 2nd approximation as an Excel spreadsheet
formula and I believe I've succeeded:
Given the ellipse's major semi-axis in B1 and
the ellipse's minor semi-axis in B2, then
=(0.5*(B1+B2))*(1+((3*((B1-B2)/(B1+B2))^2)/(10+SQRT((4-(3*((B1-B2)/(B1+B2))^2))))))
gives me results shown on that same Wiki page for the various values of b
with a value of 10000 for the major semi-axis value.

Since this particular approximation appears to be the Gold Standard of all
approximations for the circumference of an ellipse, hopefully it will suit
your needs.


"M" wrote:

Is there a formula to Calculate the Circumference of an ellipse in excel?