Metrication is complete or nearly complete in almost all countries of the world. US customary units are heavily used in the United States and to some degree Liberia. Traditional Burmese units of measurement are used in Burma. U.S. units are used in limited contexts in Canada due to a high degree of trade; additionally there is considerable use of Imperial weights and measures, despite de jure Canadian conversion to metric.
A number of other jurisdictions have laws mandating or permitting other systems of measurement in some or all contexts, such as the United Kingdom; where for example its road signage legislation only allows distance signs displaying imperial units (miles or yards)
In the United States, metric units are used almost universally in science, widely in the military, and partially in industry, but customary units predominate in household use. At retail stores, the litre is a commonly used unit for volume, especially on bottles of beverages, and milligrams are used to denominate the amounts of medications, rather than grains. Also, other standardized measuring systems other than metric are still in universal international use, such as nautical miles and knots in international aviation and shipping.
Both imperial units and US customary units derive from earlier English units. Imperial units were mostly used in the British Commonwealth and the former British Empire but in all Commonwealth countries they have been largely supplanted by the metric system. They are still used for some applications in the United Kingdom but have been mostly replaced by the metric system in commercial, scientific, and industrial applications. US customary units, however, are still the main system of measurement in the United States. While some steps towards metrication have been made (mainly in the late 1960's and early 1970's), the customary units have a strong hold due to the vast industrial infrastructure and commercial development.
While imperial and US customary systems are closely related, there are a number of differences between them. Units of length and area (the inch, foot, yard, mile etc.) are identical except for surveying purposes. The Avoirdupois units of mass and weight differ for units larger than a pound (lb.). The imperial system uses a stone of 14 lb., a long hundredweight of 112 lb. and a long ton of 2240 lb. The stone is not used in the US and the hundredweights and tons are short being 100 lb. and 2000 lb. respectively