If one assumes the egg approximates to an ellipsoid in shape (3-D oval-ish because that is the closest regular shape to an egg) , then the volume (V) of the egg can be calculated by using the formula V = 1/6 x Pi x length x width x height, where Pi is something mathematical that one can look up or just use 3.14 because it's good enough for this purpose.

So if your small egg was 5 cms in length and 4 cms wide and 4 cms deep, the approx volume would therefore be 1/6 x 3.14 x 5 x 4 x 4 = 42 cubic centimetres.

If your medium egg is just one centimetre longer i.e. 6 cms, and its width and depth are scaled up the same amount (20%), so that it is the same shape as the small egg, then its volume is 72 cubic centimetres which is 1.73 times as big as the small egg. Let's say 1.75 because it makes the math easy. A figure of 1.75 means that 4 of the medium eggs are equivalent to 7 small eggs.

If you go to the next stage and assume a large egg is 7 cms long and the same shape as the small and medium eggs then its volume is 115 cubic centimetres which is 2.74 times the volume of the smallest egg. Again let's say 2.75 between friends. And 2.75 times means that 4 large eggs produce the same sized meal as 11 small eggs (because 11/4 = 2.75).

This is why your question is such a good one. It is not sufficient to know the number of eggs to understand the size of the breakfast eaten. It is important to know the size as well.

This comment is not as good as finding money in the drier Heather but hopefully it's funnier and I haven't got any egg on my face.