UoMD - Council Directive 80/181/EEC

What UoMD is and why it matters

The Units of Measurement Directive (UoMD) — formally Council Directive 80/181/EEC on the approximation of the laws of the Member States relating to units of measurement — is the law that sets out which units may legally be used in the EU. It establishes the International System of Units (the SI system, the modern metric system) as the legal basis for expressing quantities, and it harmonises measurement across the internal market so that a kilogram, a litre or a metre means the same thing in every Member State. If your products carry any indication of quantity, length, volume, weight, area or similar — on the label, on the packaging, in instructions or in advertising — UoMD shapes how you must express it.

UoMD matters because measurement runs through almost everything a brand puts on the market: net contents, dimensions, dosages, capacities and performance figures. The Directive requires that, for economic, public-health, safety and administrative purposes, those quantities are given in legal (metric) units. Getting the units wrong is not a cosmetic issue — it is a labelling non-compliance that market surveillance and trading-standards authorities can act on, and it can block goods from sale.

📄 Official text: Council Directive 80/181/EEC on units of measurement — on EUR-Lex →

Who UoMD applies to

UoMD applies to anyone who expresses a measured quantity in the course of placing goods or services on the EU market. The duty attaches to the way information is presented rather than to a single role in the supply chain:

Manufacturers — who define net quantities, dimensions, capacities and technical specifications on the product, its packaging and in accompanying documentation.
Importers and distributors — who bring goods to EU consumers and must ensure that quantity indications on what they supply use legal units, including when they relabel or repackage.
Retailers and online sellers — who present sizes, weights and volumes in listings, on shelf-edge labels and in marketing, all of which must follow the legal-units rule.
Service providers and public bodies — because the Directive covers units used for economic, public-health, safety and administrative purposes, not only physical product labels.

In short, if a number describing a physical quantity appears in connection with trade, health, safety or administration, UoMD governs the unit it is expressed in.

Scope: what the Directive covers

UoMD covers the units used to express quantities for economic, public-health, safety and administrative purposes. That deliberately broad scope reaches product labelling, contractual documents, instruments and official measurements alike. The legal units are the SI base and derived units, together with certain other units the Directive permits, and Member States may not require quantities for the covered purposes to be expressed in non-legal units.

The Directive does not stop people from privately using whatever units they like outside these purposes; what it controls is the official and commercial expression of quantities, which is exactly where labelling and marketing live.

Core requirements

Use legal (metric) units

The central obligation is that quantities used for economic, public-health, safety and administrative purposes must be expressed in legal units of measurement — the SI system and the additional units the Directive recognises. For a brand, this means the primary indication of net contents, weight, volume, length, area and similar must be metric: grams and kilograms, millilitres and litres, millimetres, centimetres and metres, and so on. The metric figure is the one that carries legal weight and that must be present.

Supplementary indications

UoMD does allow supplementary indications — additional units shown alongside the legal metric unit. This is the mechanism that lets a label carry, for example, an imperial figure in addition to the metric one. The key conditions are that the supplementary indication is genuinely supplementary and does not displace the legal unit: the metric value must be present, and the supplementary unit must not be more prominent than it. In practice this allows brands to keep familiar non-metric figures for certain markets and audiences while the metric value remains the legally governing indication. This flexibility is particularly relevant for goods sold across multiple markets and for products that historically used non-metric units.

Consistency across labelling, instructions and marketing

Because the Directive’s scope is tied to purpose rather than to a single surface, the legal-units requirement carries through the whole presentation of a product. Net-quantity statements on packaging, dimensions in instruction manuals, capacities in technical sheets and size or weight claims in advertising all need to use legal units, with any non-metric figure handled as a supplementary indication. Treating only the front-of-pack net-quantity statement and ignoring instructions or marketing is a common gap.

Relationship with product-specific labelling rules

UoMD sets the units; other EU instruments often set how and where a quantity must be declared for a given product category. The two work together: the sector rule may require a net-quantity declaration in a particular form, and UoMD determines that the unit used must be a legal one. Brands should read UoMD alongside the relevant product-specific and consumer-information rules rather than in isolation.

Obligations by role

Manufacturers — express all net quantities, dimensions and technical figures in legal units, and treat any non-metric value as a supplementary indication that does not outweigh the metric one.
Importers — verify that goods entering the EU carry quantity indications in legal units, and correct labelling where products were prepared for non-EU markets.
Distributors and retailers — ensure shelf labels, listings and repackaged goods keep legal units as the governing indication.
Online sellers — present sizes, weights and volumes in legal units in product listings and marketing copy aimed at EU consumers.

Enforcement

UoMD is a directive, so it takes effect through each Member State’s national transposition, and enforcement sits with national authorities — typically metrology, trading-standards and market-surveillance bodies, depending on the country. In Denmark, the Danish Safety Technology Authority (Sikkerhedsstyrelsen) is the authority responsible for legal metrology and measurement matters.

The practical consequence of using non-legal units is the same kind of labelling enforcement that applies to other packaging defects: authorities can require corrected labelling, hold or refuse goods, and in some cases impose penalties set at national level. Because measurement appears on so many labels, a units error can affect an entire product range at once, which makes it a high-leverage thing to get right.

Getting compliant

Identify every place a measured quantity appears: net contents, dimensions, capacities, dosages, areas, in labelling, instructions, technical documentation and marketing.
Make the primary indication a legal (metric) unit for all of them.
Where you keep non-metric figures, present them as supplementary indications that are not more prominent than the metric value.
Check that instructions, spec sheets and advertising use the same legal units as the pack, not just the front-of-pack statement.
Read UoMD together with the product-specific labelling and consumer-information rules that apply to your category.
Re-check labelling when you take goods prepared for a non-EU market and place them on the EU market.

How Conphora helps

Conphora monitors UoMD and maps your products against its requirements, flagging where quantity indications use non-legal units or where supplementary indications risk overshadowing the metric value. The platform helps you keep labelling, instructions and marketing consistent, and alerts you when the rules change so your compliance stays current.

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Sources and further reading

This guide is for general information and is not legal advice.

Last updated: 12 June 2026