When force is applied evenly, an average of 53 pounds of force is required to crack an egg when it is standing up on its end. It takes 90 pounds of force to crack an egg on its side in the same circumstances.
The amount of force required to crack the egg depends on the surface of the egg over which the force is applied. The shape of the egg naturally helps to distribute force across the surface, making it much more difficult to break. When an egg is cracked on the side of a pan or another edge, the force is concentrated over a relatively small surface area, so it can be cracked with less force.