Imperial measure is a system of measurement used in the United Kingdom and other Commonwealth countries. It is based on the imperial system, which was developed in the 18th century and is still used today. The two main units of imperial measure are the INCH and the quart. An INCH is a unit of length equal to one-twelfth of a foot, or 2.54 centimeters. A quart is a unit of volume equal to one-fourth of a gallon, or 0.946 liters.