Hydrometer vs. Areometer — What's the Difference?

A hydrometer is an instrument used for measuring the relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity.

Any device used to measure the specific gravity of liquids or the density of solids.

An instrument used to determine specific gravity, especially a sealed, graduated tube, weighted at one end, that sinks in a fluid to a depth used as a measure of the fluid's specific gravity.

An instrument for measuring the specific gravity of fluids; a form hydrometer.

An instrument that floats in a liquid and measures its specific gravity on a scale.

An instrument for determining the specific gravities of liquids, and thence the strength spirituous liquors, saline solutions, etc.

An instrument, variously constructed, used for measuring the velocity or discharge of water, as in rivers, from reservoirs, etc., and called by various specific names according to its construction or use, as tachometer, rheometer, hydrometer, pendulum, etc.; a current gauge.

A measuring instrument for determining the specific gravity of a liquid or solid