In order for an egg to float, about 4 tablespoons of salt must be dissolved in 12 to 16 ounces of water. Typically, fresh eggs sink to the bottom of a glass of tap water.
An egg usually sinks in water because its density is greater than the density of water. Density refers to how much matter is contained within a certain volume. When salt is added to water, its density increases. Stirring the salt and water together helps them mix together more quickly. Once the density of the water is greater than the density of the egg, the egg is able to float.