What does hydrometer mean?
A hydrometer is an instrument used to measure the density or specific gravity of a liquid. Its name reflects this function: “hydro-” refers to water and the related domain of liquids, while “-meter” means a device used for measurement. In a common float-type hydrometer, a calibrated body is marked so that its level in the liquid can be read against a scale. A denser liquid generally causes the float to sit lower, while a less dense liquid allows it to sit higher. Hydrometers are used in brewing to estimate the alcohol content of wort or finished beer, in laboratories and industrial processes to monitor liquid density, and in lead-acid batteries to assess the state of the electrolyte. They are also useful in teaching the relationship among density, buoyancy, and specific gravity. Although closely related in spelling to the hygrometer, the two instruments measure different properties.
nounAn instrument for measuring the density or specific gravity of a liquid, often by observing how far a calibrated float sinks into it.
- An instrument for measuring the density or specific gravity of a liquid, especially by determining the depth at which a calibrated float floats.
"The brewer checked the wort with a hydrometer before allowing it to ferment."
"A hydrometer confirmed that the antifreeze solution still had the correct concentration."
"The technician used a battery hydrometer to check the electrolyte in each cell."
The standard plural of hydrometer.
"Several hydrometers were used to test samples from the laboratory."
A hydrometer turns an invisible property of liquid—density—into a reading you can see.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of hydrometer
Hydrometer was formed in English in the early 17th century from the Greek combining form hudro-, meaning “water,” and metron, meaning “measure.” The word therefore literally describes an instrument for measuring the density of water or other liquids. Its elements recur in related terms such as hydraulic, hydrology, and hydrogen, all of which ultimately draw on the same Greek root for water.
Related word forms
How hydrometer is actually used
This is primarily a technical term used in science, brewing, chemistry, heating, and battery maintenance. In general use, it may be encountered in educational contexts involving density or specific gravity.
Easily confused with hydrometer
A hydrometer measures the density or specific gravity of a liquid, whereas a hygrometer measures the humidity of air or another gas.