According to the science department at Elmhurst College, the density of an object is how relatively heavy an object is at a fixed volume. Mathematically, the definition of density is mass divided by volume, where the standard mass is in grams and the standard volume is in milliliters.
Less dense objects float in solvents that are more dense. Since water has a density of one gram per milliliter, any object that is less dense than water is likely to float on water. Objects with a volume in milliliters greater than their mass in grams most likely will float in water.