British law now defines each Imperial unit entirely in terms of the metric equivalent. See the
Units of Measurement Regulations 1995. This regulation effectively outlaws their usage in retail and trading except in previously established exceptions. This has now been proved by in court against the so called '
Metric Martyrs', a small group of market traders. Despite this, many small market traders still use the customary measures, citing customer preference especially among the older population.
In the United States and in a few
Caribbean countries, the
U.S. customary units, which are similar to Imperial units based upon older
English units and in part share definitions, are still in common use.
English units have been replaced elsewhere by the
SI (metric) system. Most Commonwealth countries have switched entirely to the international system of units.
The United Kingdom completed its legal transition to SI units in 1995, but a few such units are still in official use: draught beer
must still be sold in
pints, most roadsign distances are still in yards and miles, and speed limits are in
miles per hour, therefore interfaces in cars
must have miles, and even though the
troy pound was outlawed in Great Britain in the Weights and Measures Act of 1878, the
troy ounce still
may be used for the weight of precious stones and metals.
The use of SI units is increasingly mandated by law for the retail sale of food and other commodities, but most British people still use Imperial units in colloquial discussion of distance (miles and yards), speed (miles per hour), weight (stone and pounds), liquid (pints and gallons) and height (feet and inches).
In Canada, the government's efforts to implement the metric system were more extensive: pretty much any agency, institution, or thing provided by the government will use SI units exclusively. Imperial units were eliminated from all road signs, although both systems of measurement will still be found on privately-owned signs (such as the height warnings at the entrance of a multi-story parking facility). Temperatures in degrees Fahrenheit will occasionally be heard on English Canadian commercial radio stations, but only those that cater to older listeners. The law requires that measured products (such as fuel and meat) be priced in metric units, although there is leniency in regards to fruits and vegetables. Traditional units persist in ordinary conversation and may be experiencing a resurgence due to the reduction in trade barriers with the United States.
Few Canadians would use SI units to describe their weight and height, although driver's licences use SI units. In livestock auction markets, cattle are sold in dollars per hundredweight (short, of course), whereas hogs are sold in dollars per hundred kilograms. Land is surveyed and registered in metric units, but imperial units still dominate in construction, house renovation and gardening talk (although "two-by-fours" don't
actually measure 2×4", for example).
One area where Imperial units are still in current use is in firearms and ammunition. For example, Imperial measures are still used in the description of cartridge types, even where the cartridge is of relatively recent invention (e.g., .204 Ruger, .17 HMR, where the caliber is expressed in decimal fractions of an inch). In the manufacture of ammunition, bullet and powder weights are still expressed in terms of Imperial grains.
