Comparable to the shell of an egg, how thick is the earth's crust?

There are actually two layers of crust: Oceanic (4-7 miles thick) and Continental (19 miles thick). With the average radius of the earth being about 3,959 miles, that means the crust is only about 0.479% of the earth's thickness.

http://www.universetoday.com/guide-to-space/earth/radius-of-the-earth

"Yesterday I worked out the numbers. Typical poultry eggshell thickness is about 0.35 mm (as determined from some poultry journal references). The mean diameters (the arithmetic average of the long and short axes) of a set of a dozen chicken eggs from the grocery store came out at 50 mm (2 inches). The ratio of these values is (0.35/50) = (7/1000).

The Earth’s crustal varies between 8 km in the sea floors to 45 km in really mountainous continental areas. A decent estimate of average crustal thickness would be a little less than half of the average of these two numbers, as oceanic crust covers something like 70% of the Earth’s surface. So call the Earth’s crustal thickness 25 km, on average (and that’s being generous). The Earth’s diameter is 12800 km, to three significant figures. The ratio of the Earth’s crustal thickness to its diameter is therefore (25/12800) = (2/1000).

These numbers are fairly rough, but in round terms I can report that the eggshell is roughly three to four times thicker (more precisely a ratio of 7/2 = 3.5), proportionately, than the Earth’s crust."

franksanders.com/FrankSanders/Frankster's%20Blog/20A8FEC4-34B4-4956-88A5-4B1C37105A4E.html webpage no longer exists