Specific Rotation [α] is a fundamental property of optical active substances that is expressed as the angle to which the material causes polarized light to rotate at a particular temperature, wavelength, and concentration.

Because many optically active chemicals such as tartaric acid, are stereoisomers, a polarimeter can be used to identify which isomer is present in a sample – if it rotates polarized light to the left, it is a levo-isomer, and to the right, a dextro-isomer.

The optical rotation is proportional to the concentration of optically active substances in solution. A polarimetry may therefore be applied for concentration measurements of optically active substance. With a known concentration of a substance, polarimetry may also be applied to determine the specific rotation when characterizing the substance.