Hydrometer Selection Guide
Types of Hydrometers
Plain Form hydrometers do not have a built-in thermometer; a separate thermometer should be used to measure the temperature.
Combined Form hydrometers have a thermometer built-in to the body or stem to measure the temperature of the sample.
Specific Gravity is the standard scale for what a hydrometer measures. Specific gravity is the ratio of the density of your sample at 60°F to the density of water at 60°F.
Brix Scale hydrometers are used by the sugar industry. The degrees of the scale are equal to the percentage of sucrose by weight at standard temperatures.
API scale hydrometers are selected by the American Petroleum Institute (API), the United States Bureau of Mines, and the National Institute of Standards and Technology (NIST) as the standard scale for petroleum products.
Baumé hydrometers
are used for liquids heavier than water, such as syrups.
Salt hydrometers are graduated in % saturation or % by weight of salt in solution.
Alcohol (Tralle and Proof Scales) hydrometers measure directly in percentage ethyl alcohol by weight in water from 0 to 100%. The Proof scale indicates the proof of alcohol from 0 to 200 proof. Proof is twice the percentage of alcohol by volume in solution.
