Why Does an Ice Cube Float? Ice cube floats because it is lighter than water. When water freezes, it increases its volume (expands) by about one-tenth. When 10 quarts of water freeze, then, 11 quarts of ice form. Thus, ice is lighter than water and will float.
This expansion of ice also explains why one-tenth of a floating ice cube is above the surface. Ice decreases about one-tenth in size as it melts.
Therefore, the water from a melted ice cube will take up only as much space in the glass as the cube took up when it was floating. So the water level in a glass doesn’t rise as the ice melts.
The fact that ice cubes float on water tells us something important about water. When water freezes and changes into a solid, its molecules arrange themselves so that they occupy more space.