During the First World War and after the Easter Rising, Charles A Stanuell, former President of the Statistical and Social Inquiry Society of Ireland published a paper advocating the use of the metric system and a decimal currency in the UK, of which Ireland was then a part. Metrication in Ireland began in the 1970s and by 2005 was almost completed; the only exception being that the imperial pint is still used in bars for reasons of tradition. The phrase a "glass of beer" is a colloquial expression for a half-pint. All other places must sell liquids measured in millilitres and litres. Distance signs had displayed kilometres since the 1970s but road speed limits were in miles per hour until January 2005, when they were finally changed to kilometres per hour. Since 2005 all new cars sold in Ireland have speedometers that display only kilometres per hour; odometers generally became metric as well. The metric system is the only system taught in schools. Beginning in 1970, textbooks were changed to metric. Goods in shops are labelled in metric units.
Continuation of supplementary Imperial units
In 2006 it became apparent that the 2009 cut-off for the use of Imperial supplementary units could cause problems in US-EU trade. After consultation, EU Directive 2009/3/EC of 11 March 2009, among other measures, permitted:
the indefinite use of Imperial supplementary indications.
the United Kingdom and Ireland to continue the limited exemptions concerning specified uses of the pint, mile and the troy ounce, considering the absence of any impact of these exemptions on cross border trade and the principle of subsidiarity; whilst repealing the exemption for the use of acre for land registration which is no longer applied.
These amendments were published on 7 May 2009 and became effective on 1 January 2010.
Ireland continued to use imperial pipe diameters for domestic copper plumbing into the 1980s, although the pipes themselves were supplied in metric lengths - the most common diameters are half-inch and three-quarter-inch. This is in contrast to the United Kingdom where copper plumbing pipes size had been standardized to Metric units since the early 1970s, although they were, and are still, referred to by their old approximate Imperial sizes of "half-inch" and "three-quarter-inch". However, by 2020, the Irish plumbing industry has almost completely migrated to the same Metric pipework standards as used in the UK and across the European Union. The above applies only to copper pipework; plastic plumbing parts moved to Metric units at the same time as the UK.
