A hydrometer is a device the measures the density or specific gravity of a liquid. Hydrometers are calibrated based upon the specific gravity of water at 60°F being 1.000. Liquids denser than water will have a higher specific gravity, while liquids less dense will have a lower specific gravity.

To use a hydrometer, fill the test jar with the liquid to be measured. Place the hydrometer in the jar, giving it a quick twirl to dislodge any air bubbles. Once the hydrometer has settled, take the measurement reading from the scale on the side. Note: In order for the measurement to be accurate, the sampled liquid must also be at 60°F. If the liquid is not at 60°F, then the measurement must be adjusted.