Editing System of units of measurement (section)

==British imperial and US customary units==
{{Main article|Imperial and US customary measurement systems|Imperial units|US customary units}}
Both [[British imperial units]] and [[United States customary units|US customary units]] derive from earlier [[English unit]]s. Imperial units were mostly used in the former [[British Empire]] and the [[Commonwealth of Nations|British Commonwealth]], but in all these 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 [[commerce|commercial]], [[scientific]], and [[Industrial sector|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 1960s and early 1970s), the customary units have a strong hold due to the vast industrial infrastructure and commercial development.

While British imperial and US customary systems are closely related, there are a number of [[Comparison of the imperial and US customary measurement systems|differences between them]]. Units of length and area (the [[inch]], [[foot (unit)|foot]], [[yard]], [[mile]], etc.) have been identical since the adoption of the [[International Yard and Pound Agreement]]; however, the US and, formerly, India retained older definitions for surveying purposes. This gave rise to the US [[survey foot]], for instance. The [[avoirdupois]] units of mass and weight differ for units larger than a [[pound (mass)|pound]] (lb). The British imperial system uses a stone of 14&nbsp;lb, a [[long hundredweight]] of 112&nbsp;lb and a [[long ton]] of 2,240&nbsp;lb. The [[Stone (unit)|stone]] is not a measurement of weight used in the US. The US customary system uses the [[short hundredweight]] of 100&nbsp;lb and [[short ton]] of 2,000&nbsp;lb.

Where these systems most notably differ is in their units of volume. An imperial fluid ounce of 28.4130625&nbsp;ml is 3.924% smaller than the US [[fluid ounce]] (fl&nbsp;oz) of  29.5735295625 [[millilitre]]s (ml). However, as there are 16&nbsp;US&nbsp;fl&nbsp;oz to a US [[pint]] and 20&nbsp;imp&nbsp;fl&nbsp;oz to an imperial pint, the imperial pint is 20.095% larger than a US pint, and the same is true for [[gill (unit)|gill]]s, [[quart]]s, and [[gallon]]s: six US gallons (22.712470704 L) is only 0.08% less than five imperial gallons (22.73045 L).

The [[avoirdupois]] system served as the general system of mass and weight. In addition to this, there are the [[Troy weight|troy]] and the [[apothecaries' system]]s. Troy weight was customarily used for [[precious metal]]s, [[black powder]], and [[gemstone]]s. The troy ounce is the only unit of the system in current use; it is used for precious metals. Although the troy ounce is larger than its avoirdupois equivalent, the pound is smaller. The obsolete troy pound was divided into 12 ounces, rather than the 16 ounces per pound of the avoirdupois system. The apothecaries' system was traditionally used in [[pharmacology]], but has now been replaced by the metric system; it shared the same pound and ounce as the troy system but with different further subdivisions.