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Uses of Hydrometer

Last updated date: 01st Mar 2024
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What is a Hydrometer?

A hydrometer is made up of two words, hydro + meter, where hydro means water (or liquid) and meter means a scale. So, a hydrometer is used to measure some characteristics of liquids, i.e., specific gravity or relative density (density of liquid divided by the density of water). Hydrometers are filled with liquids like mercury (as in thermometers) or lead. During its use, it is placed in a container containing the liquid.

Definition: An instrument used to measure specific gravity or relative density of liquids which works on the principle that a solid body displaces its weight when placed in water and hence floats, also known as buoyancy, is called a hydrometer.

A Hydrometer Placed in a Liquid

A Hydrometer Placed in a Liquid

The value at the surface of the liquid provides the specific density of the liquid. The value of specific gravity is unitless and expressed in decimals or percentages.

Diagram of Hydrometer

Diagram of Hydrometer

Types of Hydrometers and their Uses

  • Lactometer is used for milk.

  • Alcoholometer for wines and alcohols.

  • Saccharometer for sugar.

  • A barometer for tanning liquids in leather-making.

  • Acidometer for acids.

  • Salinometer for liquids with salt content.

  • Urinometer for urine analysis.

  • Thermo Hydrometer for fuel oils like petroleum.

  • Battery hydrometer for lead-acid battery.

Application of Hydrometer in Engineering

Use in Food Industry

Use in winemaking- A saccharometer and a thermometer is used to check the amount of sugar in wine or beer. The amount of sugar that is needed to put in can be determined by its specific gravity because it increases the density of solution. The alcohol content of the end product is determined by alcoholometer.

An Alcoholometer

An Alcoholometer

Hydrometers are also used in making ice-creams and brewers.

Use in Soil Analysis

In the engineering field, the analysis of soil involves another important use of hydrometers. It is used in determining the distribution of soil particles.

Hydrometer Uses in Laboratory

Different types of specialised hydrometers are employed in different matters. All research is first done in laboratories, so the use of hydrometers in laboratories is varied.

Solved Questions

1. What is the special type of hydrometer which is used in checking the alcohol content in wine or beer?

Ans: The specialised hydrometer used for checking alcohol content is alcoholometer.

2. What do you understand about the relative density of a liquid?

Ans: Relative density of a liquid means density of liquid divided by density of water.

3. In what units is the specific gravity measured?

Ans: Specific gravity does not have any unit, it is unitless.


A hydrometer is an instrument used to measure the relative density or specific gravity of a liquid. It is of great importance for our day-to-day life as it is used in various industries which are crucial for our health. There are different types of specialised hydrometers which are named after their use.

FAQs on Uses of Hydrometer

1. Are there different types of hydrometers?

Yes, there are various specialised hydrometers.

2. Are hygrometer and hydrometer the same?

No, hygrometer is used to measure humidity in air whereas hydrometer is used to measure specific gravity of a liquid.

3. Is a thermometer also a type of hydrometer?

Yes, it is also used to measure temperature.

4. In what type of liquid does a hydrometer rise more?

In dense liquids like salt water solution, a hydrometer gives a higher value.

5. Why do hydrometers not have any units?

It compares the density of the liquid to the density of water; therefore, the scale of the hydrometer does not have any units.