Figuring Area In A Dome Ceiling
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Old 10-18-2006, 09:55 PM   #1
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Figuring Area In A Dome Ceiling

Can anybody tell me (or where to find it) the formula for calculating sq ft for the interior surface of a dome (concave) ceiling?
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Old 10-18-2006, 09:57 PM   #2
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Re: Figuring Area In A Dome Ceiling

Wouldn't it be half a sphere or some fraction there-of?

Area=4*3.1416*Radius squared

edit, not a roof. OK just figure out how much of the sphere it is, as a percentage.
Last edited by Tscarborough; 10-18-2006 at 10:01 PM.
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Old 10-18-2006, 10:07 PM   #3
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Re: Figuring Area In A Dome Ceiling

That formula just made my brain smoke. Man, I feel stupid tonight.
Say I have the prints, and I know the diameter of the ceiling, and the height from the topmost point, to the bottom edge of it. Can I figure it that way?

BTW, I don't know yet if it is half a sphere, of really how shallow/steep the the curvature will be. Would that be considered the 'degree' of curve?
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Old 10-18-2006, 10:13 PM   #4
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Re: Figuring Area In A Dome Ceiling

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Originally Posted by Tscarborough View Post
Wouldn't it be half a sphere or some fraction there-of?

Area=4*3.1416*Radius squared

edit, not a roof. OK just figure out how much of the sphere it is, as a percentage.
That's only assuming it's a perfect half sphere. I did a quick search and it seems this would do the calculations for you.

http://www.monolithic.com/plan_design/calcs/index.html
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Old 10-18-2006, 10:15 PM   #5
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Re: Figuring Area In A Dome Ceiling

Bingo, PWG, there is your calculator, no brain smoking needed.
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Old 10-18-2006, 10:17 PM   #6
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Re: Figuring Area In A Dome Ceiling

½(4¶r²)
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Old 10-18-2006, 11:01 PM   #7
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Re: Figuring Area In A Dome Ceiling

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That's only assuming it's a perfect half sphere. I did a quick search and it seems this would do the calculations for you.

http://www.monolithic.com/plan_design/calcs/index.html
Great link, I appreciate that. Now, can anybody explain to me what the two terms mean (or how I can find these numbers out) major radius, and minor radius? These are mentioned on the oblate ellipsoid.
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Old 10-18-2006, 11:06 PM   #8
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Re: Figuring Area In A Dome Ceiling

Don't know how you can find them out........but the minor and major are the lengths of the minor and major axis(major being the larger one)....because an ellipse has two different lengths of axis's.
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Old 10-19-2006, 06:39 AM   #9
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Re: Figuring Area In A Dome Ceiling

Wow....back to geometry again...I thought the major radius is drawn on the convex, and the minor is the true radius? Now I need to go look.
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Old 10-19-2006, 09:57 AM   #10
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Re: Figuring Area In A Dome Ceiling

I think you are somewhat on the right track. I can't remember either. Usually, we find them in 2D....instead of thinking of them in 3D. The minor is usually the shorter axis....which I'd think of as the length of the height.....and I'd say the major is the length of the circle.

Heres another site to look at, if you can understand it. It took me a while......about half way down, it talks about P,R,Q(thats the section to look for).

I've only figured ellipses on the earth and its rotation, so I'm not sure about these ones.
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Old 10-19-2006, 09:59 AM   #11
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Re: Figuring Area In A Dome Ceiling

Did anyone bother to scroll down on the calculator page.....it pretty well describes everything down past the calculator.....I think.
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Old 10-19-2006, 11:57 AM   #12
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Re: Figuring Area In A Dome Ceiling

Quote:
Originally Posted by Tscarborough View Post
...sphere...Area=4*3.1416*Radius squared...
Yes.


Quote:
Originally Posted by Bradracer18 View Post
...the minor and major are the lengths of the minor and major axis(major being the larger one)....because an ellipse has two different lengths of axis's...
Yes.



Quote:
Originally Posted by joasis View Post
..I thought the major radius is drawn on the convex, and the minor is the true radius?...
No.
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Old 10-19-2006, 02:16 PM   #13
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Re: Figuring Area In A Dome Ceiling

Man, you guys are REALLY overthinking this. Why not just take the area of the circle at the low point, and double it? That should give you plenty of paint, and even if you're off by a little bit, who cares? Unless we're talking about the inside of the Superdome, you couldn't possibly miss by enough to make it worth any more effort.

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Old 10-19-2006, 02:39 PM   #14
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Re: Figuring Area In A Dome Ceiling

Bob, this isn't for paint. It is for a digitally printed mural we have been asked to install in a historical building in New Orleans. I don't think it will be my probelm to figure out the sq ft for printing, just trying to figure it out for my own use, so I can track my sq ft installation rates.
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Old 10-19-2006, 03:52 PM   #15
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Re: Figuring Area In A Dome Ceiling

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Man, you guys are REALLY overthinking this. Why not just take the area of the circle at the low point, and double it? That should give you plenty of paint, and even if you're off by a little bit, who cares? Unless we're talking about the inside of the Superdome, you couldn't possibly miss by enough to make it worth any more effort.

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Old 10-19-2006, 07:21 PM   #16
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Re: Figuring Area In A Dome Ceiling

I know what you mean Mike. I once calculated the size of a 24 gal. hydraulic tank to be installed in a given space in my head. I was off by .24 gal. when we worked it out on paper.
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Old 10-19-2006, 07:31 PM   #17
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Re: Figuring Area In A Dome Ceiling

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hydraulic tank to be installed in a given space in my head.

You had a hydraulic tank installed in your head??
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Old 10-19-2006, 08:15 PM   #18
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Re: Figuring Area In A Dome Ceiling

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You had a hydraulic tank installed in your head??
24.. that's twenty-four gallons.
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Old 10-19-2006, 08:17 PM   #19
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Re: Figuring Area In A Dome Ceiling

That's a big head.
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Old 10-19-2006, 08:36 PM   #20
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That's a big head.
And thats a gimme.
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