Units of measurement in the EU

Directive 80/181/EEC on the approximation of EU countries’ laws relating to units of measurement

It lists and defines the legal units that must be used to express quantities in the European Union (EU). It specifies that the metric units of measurement / International System of Units (SI units)* are applicable in the EU.

Council Directive 80/181/EEC has been amended several times. The last one, introduced by Commission Directive (EU) 2019/1258 for the purpose of its adaptation to technical progress, amends the annex as regards the definitions of SI base units.

Key Points

SI units are mandatory in the EU for economic, public-health, public-safety and administrative purposes.

SI units originated from international resolutions adopted by the General Conference on Weights and Measures (CGPM) to which all EU countries adhere.

The directive lists and defines the permitted and mandatory units of measurement in a series of annexes, including the following.

The SI base units

Time: the second (s).
Length: the metre (m).
Mass: the kilogram (kg).
Electric current: the ampere (A).
Thermodynamic temperature: the kelvin (K).
Amount of substance: the mole (mol).
Luminous intensity: the candela (cd).

Over 20 SI-derived units, with special names and symbols (e.g. Frequency: hertz (Hz), Force: newton (N), Electric resistance: ohm (Ω)).
The prefixes designating decimal multiples and submultiples (e.g. Kilo: 103 and k, Milli: 10-3 and m).
Units permitted in specialised fields only (e.g. Vergency of optical systems: dioptre, Mass of precious stones: metric carat).

Compound units.

The definitions of the units are based on natural constants, allowing for accurate measurements even on a very small scale. As such, they can be used not only in everyday life, but also for purposes requiring very high precision, like scientific research or advanced technological applications.

Exemptions: The directive does not affect the use of units in air and sea transport and rail traffic as laid down in international agreements binding the EU or EU countries.

Derogations are only applicable in Ireland and in limited circumstances:

the mile, yard, foot and inch continue to be permitted on road traffic signs and for distance and speed measurements;
pints continue to be permitted for the sale of milk in returnable containers and draught beer and cider;
troy ounces can continue to be used for precious metals.

Supplementary indications

The directive also allows the use of supplementary indications (those of quantity expressed in units of measurement not contained in the directive). They cannot, however, be used by themselves; they can only accompany the SI units listed and defined in the directive and the SI units have to predominate.


It has applied since 1 October 1981 and had to become law in the EU countries by 1 July 1981.

BFor more information, see:

Units of measurement (European Commission)
General Conference on Weights and Measures (BIPM-CGPM)
International Organization for Standardization (ISO).

International System of Units (SI): a system of physical units of measurement based on the metre, kilogram, second, ampere, kelvin, candela, and mole, together with a set of prefixes to indicate multiplication or division by a power of 10. It is the modern form of the metric system and the only system of measurement with an official status in nearly every country in the world.


Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC (OJ L 39, 15.2.1980, pp. 40-50)

Successive amendments to Directive 80/181/EEC have been incorporated into the original text. This consolidated version is of documentary value only.


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