What is a refractometer and how does it work?

Woman using refractometer

Refractometer FAQs

What is a Refractometer?

A refractometer is a simple instrument used for measuring concentrations of aqueous solutions such as gases, liquids, and translucent solids. Different types of refractometers are available depending on the application. Refractometers can be handheld, compact, benchtop, Abbe, and Brix as well as different types for measuring materials such as salt, sugar or battery acid.

What is a refractometer used for?

Refractometers are used in the laboratory and in many industries including agricultural, food, chemical, and manufacturing industries.

In the lab, refractometers measure the composition of samples from many industries. Some refractometers are designed for challenging samples and provide highly precise measurements.

In the food industry, refractometers have many uses including measuring sugar and salt. In winemaking, Brix refractometers can check the sugar content of the grape juice. Sugar can be measured in a jelly and jam, milk, fruit juice, and other types of beverages. Salt content can be measured in brines, cheese, or even in bakery items.

In agriculture, beekeepers use refractometers to check the moisture in honey. Refractometers can also measure the water content of milk or for determining concentration of soy milk.

Refractometers can also measure chemical concentrations, validate mixtures and determine the purity of materials.

In manufacturing, inline process refractometers provide composition of substances, control dilution, and check for the purity of a substance.

What does a refractometer measure?

Using these values, you can determine the concentrations of solutions. For example, solutions have different refractive indexes depending on their concentration in water.

prism in a refractometer

The prism in the refractometer has a greater refractive index than the solution. Measurements are read at the point where the prism and solution meet. With a low concentration solution, the refractive index of the prism is much greater than that of the sample, creating a large refraction angle and a low reading ("A" on diagram). The reverse would happen with a high concentration solution ("B" on diagram).

What are the types of refractometers?

Handheld refractometers are the most commonly used. They are compact analog instruments that fit neatly in the palm of your hand and provide quick and effortless operation with reliable measurements.

Digital refractometers feature an easy-to-read LCD, eliminating reading errors that can occur when using analog handheld refractometers.

Abbe refractometers are the larger bench laboratory refractometers that provide highly accurate measurements of refractive index and Brix measurements of liquids and solids.

What is a Brix Scale and Brix percentages?

The Brix scale is calibrated to the number of grams of cane sugar contained in 100 mL of water. Therefore, the Brix % reading equals actual sugar concentration.

Sample fluid Brix %
Cutting oils
Carbonated beverages
0 to 8
4 to 13
5 to 15
11 to 18
Grapes and wines
Concentrated juices
Condensed milk
Jams and jellies
14 to 19
42 to 68
52 to 68
60 to 70

Common refractive indexes

Refractive index readings are temperature-dependent.

Sample fluid Temperature Refractive
Acetic acid
Paraffin oil
Palm oil
Olive oil
Methyl salicylate
Methyl iodide

How to read the refractometer meter results

It’s easy to use a refractometer and best to consult your manufacturer’s manual for exact instructions. For general purposes, always calibrate the refractometer first with distilled or deionized water to zero the instrument and the proper refractive index calibration solution . Then, when ready to use, place about 3 to 5 drops of liquid on the prism. If there is a cover, close the cover. For handheld analog instruments, point prism end toward the source of light. Focus in and read the scale value at the point where the light meets the dark area of the scale. Some benchtop meters will have a crosshair area for viewing the results.

For a digital instrument, zero the instrument with distilled or deionized water, calibrate the instrument with a known standard. Then add 3 to 5 drops of your liquid. Wait for the instrument to read and display the results. An illuminated light source provides light for the reading. Read the manufacturer’s manual for exact use.


A refractometer is a handy instrument that can be used to measure samples in a lab, sugars in a food, composition of chemicals and control dilution in a manufacturing in-line process. Whatever your application, be sure you select the right refractometer for you needs.