Math Help: Surface area of an oval?

[kklaric]

Dear All,

I need some help calculating the area of an oval.

If I have an oval that is 5" x 7" what is the surface area?

Is it greater than or less than the surface area of a 6.5" circle? (pi*(6.5/2)^2=33.18")

Thanks,

David.

[Wood Butcher]

A = Pi * a * b where a & b are the semimajor(half the long) and semiminor(half the short) axes.

Art

[Angelo Castellano pos]

[Victor Radin]

I couldn't remember, but curiosity got the better of me so- did a quick search and found this:

it's for pools, but it seems to work if you plug in 0 for depth.

Vic

btw- it works out to be 29 for the oval, and 34 for a 6.5 round.

[kklaric]

Hello Art,

So my 5"x7" oval is 27 square inches? (pi*(7/2)*(5/2)

Thanks,

David.

[Leon]

AutoCAD calls it 27.4889 . A 6.5 circle has 33.183 sq. in.

[xrongor]

you didnt say how close it needs to be, but if it needs to be close, everyone is assuming you have an ellipse and the formula that has been given is based on that assumption. an ellipse has definition involving foci and such. it is possible to have an oval shape that is not an ellipse.

for truly irregular shapes, its probably best to use graph paper and just start counting squares. the closer it needs to be, the smaller the squares on the graph paper. OR you could get tricky and start dunking the thing in water and start calculating area based on displacement.

anyway, fair warning about using that formula. or maybe you meant to say ellipse.

randy

[Doug Miller]

Do you mean an ellipse (a "stretched" circle, for lack of a better description), or an oval (a rectangle with the corners rounded off)?

If you mean an ellipse, the area is pi * (a/2) * (b/2) = pi * 5/2 * 7/2 = 27.5 square inches.

If you mean an oval, the area is between 29.6 and 35 square inches, depending on the radius of curvature of the corners.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

For a copy of my TrollFilter for NewsProxy/Nfilter, send email to autoresponder at filterinfo-at-milmac-dot-com