gram per cubic centimeter

The gram per cubic centimetre exists to make water the yardstick. With water at essentially 1, every value doubles as a specific gravity: seawater 1.025, milk about 1.03, lead-acid battery electrolyte 1.265 when fully charged, gold 19.3. That is why a hydrometer floating in a flooded battery reads state of charge directly, and why brewers and winemakers track a fermentation by watching the specific gravity fall as dense sugar becomes lighter alcohol.

Ice at 0.917 g/cm³ is the strange entry. Almost every substance densifies on freezing; water expands, which is why ice floats with about 90 percent of its bulk submerged, why unprotected pipes burst, and why lakes freeze from the top down and keep their fish alive underneath. The planetary version of the same comparison: Saturn's mean density is 0.69 g/cm³, the only planet in the solar system less dense than water, the standard illustration being that it would float in a sufficiently large bathtub.

This is the chemistry-lab native unit, and the conversion trap runs both directions: multiply by exactly 1000 to reach kg/m³, so aluminium's 2.70 becomes 2700. Mineral identification still leans on the number, because density is measurable with nothing but a balance and a displacement beaker. Archimedes' method, which began with a question about a crown, remains the fastest test of whether a gold-coloured object actually has gold's 19.3.