What is Density?

All You Need to Know About Density Measurement

Density Measurement

What is Density? - How to measure Density? – What are the main applications of Density?

In this video, you will become an expert on how to measure density of liquids and the best methods to measure it.
Difference in Density


Balance with density kit



A hydrometer is a cost-effective instrument used to determine the density of liquids. Made of blown glass, it consists of a bulbous bottom weighted with lead or steel shot and a long, narrow stem with a scale. The hydrometer is immersed into the sample liquid until it floats. The density reading is taken by looking at the scale, where the level of the sample liquid aligns with a marking on the hydrometer scale. Most hydrometers measure the specific gravity of samples: in simple terms, a hydrometer tells the user if a liquid is denser or less dense than water. It will float higher in a liquid with a greater specific gravity, such as water with sugar dissolved, compared to one with a lower specific gravity, such as pure water or alcohol.

When using a hydrometer, the user has two options:

  1. Use the hydrometer at its calibration temperature (usually 16 °C or 20 °C). Depending on the sample volume, it can take some time for the sample to reach this temperature.
  2. Simply record the measurement value at the surrounding temperature. Both measurement and temperature values must be recorded. If needed, a correction factor can be applied later to obtain the temperature-corrected measurement value.



Typically made of glass, a pycnometer is a flask of a pre-defined volume used to measure the density of a liquid. It can also determine the density of dispersions, solids, and even gases. When used correctly, pycnometers provide very precise results, with accuracy up to 10-5 g/cm3 – this correlates with the accuracy (number of decimal places) of the digital balance used. A thermometer is also required to measure the temperature. User training is required to guarantee accurate measurements with the pycnometer.

Portable Digital Density Meter

Portable digital density meter
Portable digital density meter

Portable digital density meters are used to quickly and accurately determine the density of liquids. Determination of density using digital meters is based on two factors:

  1. The oscillation, or vibration, of a U-shaped glass tube (U-tube).
  2. The relationship between the liquid sample mass and the frequency of oscillation of the U-tube. Filling the U-tube with sample liquid affects its frequency of oscillation: due to factory adjustment with samples of known densities, this frequency of oscillation can be directly correlated with the density of any liquid sample with an accuracy of 0.001 g/cm3. Handheld digital density meters measure the sample at ambient temperature. If a result is needed at a certain temperature, the digital density meter can apply a correction factor to the measured result to compensate the result to a defined temperature. Each measurement takes only a few seconds, allowing users to move on to the next sample quickly. The measured density can be automatically converted into other units and concentrations for specific applications, such as specific gravity, API, alcohol%, °Brix, etc.

Benchtop Digital Density Meter

Benchtop digital density meter
Benchtop digital density meter

Benchtop digital density meters use the same technology as portable digital density meters, the oscillation of a U-shaped glass tube (U-tube). In addition, they feature a built-in Peltier temperature control, which brings the sample to the selected temperature (e.g., 20°C). The temperature control can range from 0 °C to 95 °C. These density meters can reach an accuracy of 0.000005 g/m3 for density.

Some benchtop digital density meters can be connected to sample automation solutions for single or multiple samples, which offer automated sampling, rinsing, and drying. These density meters can often be upgraded into a dedicated automated multi-parameter system combining density, refractive index, pH, color, conductivity, and more to save time, increase data quality, and prevent any alteration of samples between individual analyses.

One of the benefits of digital density meters using the U-shaped glass tube is the small volume of sample required (typically 1.5 mL), which allows for a faster temperature equilibrium of the sample.

Manual to Digital Density Measurement

Density vs. Temperature
Density vs. Temperature


d ethanol at 20°C = 0.7895 g/cm³

d ethanol at 40°C = 0.7724 g/cm³


d water at 20°C = 0.9982 g/cm³

d water at 40°C = 0.9922 g/cm³


SG ethanol at 20°C = 0.7909 g/cm³

SG ethanol at 40°C = 0.7785 g/cm³

Molecules at lower temperature
Molecules at lower temperature

Molecule at a given temperature
(slight movements)

Molecules at higher temperature
Molecules at higher temperature

Same molecule when temperature increases
(moving further apart)

How to calibrate a pycnometer
Glass Pycnometer
Hot air balloon
density determination
Viscosity in density
Density vs viscosity curve
Relative density definition
Specific gravity definition
True density or absolute density definition
Apparent density definition

To illustrate the difference between true density and apparent density, we have a pycnometer placed onto a balance. When it is filled with a liquid, it weighs less in air than in a vacuum due to the buoyancy effect of air.

Many official density tables are still based on apparent density. Digital density meters deliver results in different units and concentrations, check out their specifications.

Mass in vacuum=True density
Mass in vacuum = True density
Mass in air=Apparent density
Mass in air = Apparent density
Specific Gravity
(at 20°C)
(at 20°C)
0.7460.745 g/cm3
0.7720.771 g/cm3
0.7910.790 g/cm3
1.0000.998 g/cm3
1.2511.249 g/cm3
1.2611.259 g/cm3
1.4841.481 g/cm3
13.61813.593 g/cm3

At Different Temperatures

Density (at 15°C)SG (at 25°C)Density (at 25°C)
0.752 g/cm30.7470.745 g/cm3
0.999 g/cm31.0000.997 g/cm3
1.254 g/cm31.2481.244 g/cm3
1.486 g/cm31.4801.476 g/cm3


What is the difference between density and mass?

Mass is a measure of how much matter there is within an object or liquid while density expresses how much mass there is per a certain amount of volume.

For example, 10 kg of steel and 10 kg of feathers have the same mass, but different volumes therefore they have different densities.


Why can density be used to identify a sample?

Density can easily be used to identify a pure sample because each element has a unique density. After a measurement, the density of the sample in question can be looked up to see what it corresponds to.


How is the density of solutions measured?

Let's take a solution of ethanol in water as an example.

As shown before, at 20 °C pure water has a density of d = 0.9982 g/cm3, and pure ethanol has a density of d = 0.7892 g/cm3 at 20 °C. A solution of ethanol/water will have a density value which depends on the concentration of the solution.



Is density directly proportional to pressure?

Density is directly proportional to the local air pressure but indirectly proportional to temperature. At a constant temperature, when pressure increases density increases. Learn more about the relationship between density of liquids and pressure here.



What are some typical applications of density measurement?

Wort Measurement in Beer Application


Some applications of density measurement includes the determination of alcohol concentration in spirits, control of fermentation process in wine and beer production, Brix (sugar content) measurement of intermediate and final products in food and beverages products. Density and other concentration as API gravity in heavy oils, paraffin and lubricants in the Petrochemical segment. Density (specific gravity) in battery acid in the automobile industry, as well as other solvents, acids and bases in the chemical industry. Lastly, there are many applications in the pharmaceutical industry, such as the density measurement of specific gravity in cosmetics, personal care products, and many more. Click on the links above to read our detailed applications or access our expertise library to find the right application note according to your sample.



What is the density of air?

The density of air is 0.00120 g/cm3 at 20°C and under atmospheric pressure of 101.325 kPa (i.e. at sea level). This atmospheric pressure changes with the weather conditions (lower pressure when rainy or snowy) and with the altitude (lower pressure at high altitude than at sea level). At an elevation of 440 m above sea level, for example, the atmospheric pressure (yearly mean) is 96.12 kPa only and the mean air density becomes 0.00114 g/cm3 at 20°C.

Learn more



What is the density of water?

The density of water is 0.99820 g/cm3 at 20°. The density of water changes with the temperature. It increases from 0°C to 4°C (where it is nearly 1) and then decreases from 4°C to higher temperatures.



What is the influence of viscosity on digital density measurement?

Sample viscosity has an impact on the density measured with a digital density meter. The higher shear force which occurs between the fluid and the tube wall results in slowing down the oscillation frequency, thus showing a higher density value. Modern digital density meters therefore have a built-in viscosity correction, which compensates for this effect to show correct results.