How big an egg can be? Please hold on to flag as off-topic.
Few days ago I received a question - how big an egg can possibly big? Can it be as big as 1 meter, as a human? (Imagining that there could be really huge animals which would lay these eggs)
My thoughts are that an egg should have an upper limit and basically you can find out the biggest possible egg for Earth. By big I assume the biggest volume.
I started to think this way - the thing inside the egg should breath, therefore the egg should allow CO2 and O2 to go in and out. The thing inside the egg consumes constant amount of O2 which is related to the volume of the egg. On the other hand the surface of the egg is related to the amount of air the baby can breath. But with the increase of the size of the egg - the volume is growing much faster then the surface. So at some point of time the amount of air going inside of the egg would not be enough.
I think that I am on the right track, but can not finish it to receive the answer.
P.S. I hesitated about the Math.stackexchange and physics, but assumed that this one is more applicable but please feel free to move it to math if you think it is better
 A: This question should be posted on biology stack exchange, because the limiting issues turn out to be biological rather than physics. 
For an outside-the-mother egg (i.e. a laid one rather than one, say, kept inside the body of a viviparous snake or even the ovum of a mammal), your reasoning is very sound physics and your ideas on gas exchange are very much on the right track, but it turns out not to be the surface area to volume ratio that limits an egg.
It's simply the mechanical strength of the shell. The shell cannot be too thick - otherwise there wouldn't be quick enough gas diffusion across it, although this turns out to be the lesser issue. The main one is the need for the baby to break out. 
We know this because ostrich eggs and those of hugely bigger creatures (i.e. sauropod dinosaurs - at least all the ones we've found and can be sure which animal they are from) are pretty much the same size and have very like shell thicknesses.
My source is David Attenborough videos and my seven year old daughter - although the latter is highly reliable, I don't know her primary sources. So, like I said, this would be a good question to post on biology stack exchange.
