What is the difference between MID 2014/32/EU and NAWI 2014/31/EU?

MID (Measuring Instruments Directive) covers ten categories of measuring instruments listed in Annex IX and numbered MI-001 to MI-010: water meters, gas meters, active-energy electrical meters, heat meters, fuel dispensers, automatic weighing instruments, taximeters, material measures, dimensional measuring instruments, and exhaust-gas analysers. NAWI (Non-Automatic Weighing Instruments) covers only non-automatic weighing instruments, that is, those requiring operator intervention during weighing (shop scales, laboratory balances used for trade). Both directives are parallel, of the same date, aligned on Decision 768/2008/EC.

Which instruments fall under MID and which do not?

MID applies to instruments used for legal-metrology functions, that is, commercial transactions, public-interest measurements, fiscal and customs declarations, or occupational health and safety. A water meter installed in a private home and billed by the distributor falls under MID. The same device used only for internal self-consumption tracking, without third-party billing, does not. The "own use" versus "commercial use" distinction is decisive and conditions the rest of the compliance pathway.

What is Maximum Permissible Error (MPE) and accuracy class?

The Maximum Permissible Error (MPE) is the maximum allowed deviation between the indicated value and the true value, expressed as a percentage or as an absolute value depending on the category. The accuracy class groups instruments by applicable MPE level. The exact values are set by MID-specific annex (MI-001 for water meters, MI-002 for gas meters, and so on) and are not transferable from one category to another. MID always distinguishes the in-service MPE (initial verification or in operation) from the MPE under reference conditions.

What is the format of the M marking and what does it certify?

A MID-compliant instrument carries two combined markings: the classic CE marking and the supplementary metrology marking, consisting of the letter "M" followed by the two-digit year and the four-digit identification number of the Notified Body that participated in the evaluation (for example "M26 0123"). The absence of the M marking on an instrument that falls under MID is a serious non-conformity: an instrument sold with the CE marking only cannot be used for legal-metrology purposes. The M marking attests specific conformity to MID requirements.

Which conformity assessment modules are allowed under MID?

MID lists, in its Annex II, the authorised modules within the 768/2008/EC framework. The most frequent combinations are B+D (EU-type examination plus production quality assurance), B+F (examination plus product verification), H1 (full quality assurance with design examination) and G (unit verification). Each annex MI-001 to MI-010 restricts the list to the modules relevant to the category. Notified Body involvement is mandatory for virtually all categories: pure module A (self-declaration) is generally not available.

What does WELMEC 7.2 say about embedded software in measuring instruments?

WELMEC 7.2 is the consolidated European guide on software in measuring instruments. Published by WELMEC (European Cooperation in Legal Metrology), it describes the requirements applicable to embedded, separate and downloaded software to ensure stability of the metrology functions, data integrity, traceability of updates, and separation between legally relevant and non-legally relevant functions. Notified Bodies rely on WELMEC 7.2 to assess software documentation. A MID instrument whose software does not follow the WELMEC 7.2 doctrine is rarely certified.

What is the link between MID and OIML recommendations?

OIML (International Organisation of Legal Metrology) publishes international recommendations (the "OIML R" series) that serve as the technical foundation for most national legal-metrology regulations, including MID. Each MI-00x category references at least one OIML recommendation: R 49 for water meters, R 137 for gas meters, R 46 for active-energy meters, R 75 for heat meters, R 117 for fuel dispensers, R 51 and R 61 for automatic weighing instruments, R 21 for taximeters. OIML certificates facilitate international acceptance but do not waive MID conformity for the European market.

Do smart meters fall under MID?

Yes. A communicating active-energy electrical smart meter falls under MID category MI-003 for its metrology functions, and remains subject to other European directives for its non-metrological functions: RED 2014/53/EU for the radio part, EMC 2014/30/EU for electromagnetic compatibility, GDPR for personal consumption data, and the forthcoming Cyber Resilience Act for software security. MID covers metrology stability and energy-counting integrity; it does not cover data privacy or cybersecurity.

MID 2014/32/EU: Measuring Instruments (MI-001 to 010)

Author Hugues Orgitello Last updated 27 May 2026 ~14 min read

Guide. European legal metrology

Directive 2014/32/EU, known as MID (Measuring Instruments Directive), governs measuring instruments used for legal-metrology purposes in the European Union: commercial transactions, public-interest measurements, fiscal and customs declarations, occupational health and safety. It replaced Directive 2004/22/EC to align with the New Legislative Framework. Annex IX of the directive enumerates ten categories of instruments covered, numbered MI-001 to MI-010, ranging from water meters to exhaust-gas analysers. This page sets out the scope, the essential requirements, the categories, the authorised assessment modules, the M metrology marking, and the articulation with WELMEC, OIML and the NAWI sister directive.

The scope of legal metrology

Legal metrology covers measurement activities subject to a regulatory framework because their results carry legal or financial weight. Directive 2014/32/EU formalises four domains:

Commercial transactions: billing of the end consumer or between operators, supermarket cashier scale, domestic water or gas meter, fuel dispenser at a service station.
Public-interest measurements: protection of public health, environment and safety, air-quality or emissions monitoring, control of water for human consumption.
Fiscal or customs measurements: declaration of volumes or masses for the calculation of taxes, customs duties, and excise.
Occupational health and safety measurements: measuring equipment mandated by labour regulation (for example exposure measurements).

The directive does not apply to instruments used for internal control with no legal effect on third parties. An energy meter installed by a company to track its own consumption, without third-party billing or regulatory declaration, is outside scope. This "own use" versus "legally relevant use" distinction is decisive: it triggers the applicability of MID and the obligation of a Notified Body.

The ten categories of Annex IX

Annex IX of the directive enumerates the ten categories of instruments covered, each detailed in an annex MI-001 to MI-010 that sets the specific requirements, the rated operating conditions, the maximum permissible errors, the relevant accuracy classes and the authorised conformity assessment modules.

Synoptic table of MI categories

Annex	Category	Examples of instruments	Reference OIML recommendation
MI-001	Water meters	Domestic and industrial cold and hot water meters	OIML R 49
MI-002	Gas meters and volume conversion devices	Residential, commercial and industrial gas meters, PTZ converters	OIML R 137, OIML R 140
MI-003	Active-energy electrical meters	Standard and smart electrical meters	OIML R 46
MI-004	Heat meters	Heat meters, cooling meters, calorimeters	OIML R 75
MI-005	Continuous and dynamic measuring systems for quantities of liquids other than water	Fuel dispensers, petroleum-product metering, liquid chemical-product metering	OIML R 117
MI-006	Automatic weighing instruments	Catchweighers, gravimetric fillers, rail weighbridges, automatic weighbridges	OIML R 51, R 61, R 106, R 107
MI-007	Taximeters	Taximeters associated with motion-signal sensors	OIML R 21
MI-008	Material measures	Length material measures, capacity-serving measures (standardised wine glasses, jugs)	OIML R 138 and others
MI-009	Dimensional measuring instruments	Multi-dimensional length measuring instruments, area measuring instruments, cable-length meters, leather-area meters	Various OIML recommendations
MI-010	Exhaust-gas analysers	Vehicle exhaust-gas analysers used in technical inspection	OIML R 99

How to read the table: each line refers to a dedicated annex within Directive 2014/32/EU. The directive does not set the same accuracy thresholds for two distinct categories; the corresponding MI-00x annex must be consulted for the exact accuracy-class and MPE values. The presence of a category in Annex IX does not exhaust the obligations: a water meter used in industrial settings must also comply with cross-cutting directives (EMC, LVD if mains-powered, RED if it transmits by radio).

The essential requirements of Annex I

Annex I of MID defines the cross-cutting essential requirements applicable to all instruments. They form the common core that the specific annexes MI-001 to MI-010 then refine.

Accuracy and maximum permissible error

The instrument must maintain its accuracy under the rated operating conditions specified by the directive and the specific annexes. The directive distinguishes:

The maximum permissible error (MPE) under reference conditions: applicable for initial verification and subsequent verification, in a metrology laboratory.
The maximum permissible error in service: applicable in operation, generally wider than the reference MPE to account for drift and real-world conditions.
The accuracy class: group of instruments sharing the same MPE and the same rated operating conditions.

The exact values are not set by the general Annex I: they are set instrument by instrument in the MI-001 to MI-010 annexes and in the referenced OIML recommendations. Any specific MPE figure must be supported by the MI-specific annex.

Reproducibility, repeatability, sensitivity and resolution

The instrument must provide results that are reproducible over time, repeatable for a given measurement, sensitive to significant variations of the measured quantity, and with a resolution sufficient for the declared accuracy class. These notions are defined by the international vocabulary of metrology (VIM, IEC 60050-300 and JCGM 200).

Influence of external factors

Annex I requires the control of four families of influence factors on metrology performance:

Climatic factors: ambient temperature, humidity, atmospheric pressure. The MI annexes specify the rated ranges (for example -10 to +55 Celsius for outdoor water meters).
Mechanical factors: vibration, shock, position. The directive cites mechanical classes M1, M2, M3 calibrated on exposure level.
Electromagnetic factors: electromagnetic compatibility under the European harmonised standards. The directive defines classes E1, E2, E3 according to the required EM immunity level.
Supply-related factors: voltage, frequency, harmonics, micro-interruptions for mains-powered instruments; voltage, current, durability for battery-powered instruments.

Conformity assessment must demonstrate that the instrument meets MPE under all admissible combinations of these factors, not only under laboratory conditions.

Durability

The instrument must keep its metrology characteristics over the typical lifetime of the category. The directive requires a long-term stability demonstration through accelerated testing or documented field experience. The MI annexes set category-specific criteria (for example a water meter must retain its accuracy class after ten years of typical use).

Reliability and failure indication

The instrument must signal any malfunction that would take it outside the MPE, either by explicit display or by blocking the measurement function. Annex I requires that a malfunction must not result in an erroneous measurement presented as valid.

Protection against manipulation

The metrology functions must be protected against unauthorised manipulation, either by physical sealing or by software sealing (passwords, signatures, logs). It is on this point that WELMEC 7.2 elaborates the requirements applicable to software.

Documentation, markings, instructions

The technical documentation, the mandatory markings and the user instructions must allow the user and the surveillance authority to identify the instrument, its accuracy class, its rated conditions and the verification procedure.

Conformity assessment modules

MID, like all "new approach" directives revised in 2014, aligns with Decision 768/2008/EC for its assessment modules. Annex II of Directive 2014/32/EU lists the authorised modules, and each annex MI-001 to MI-010 restricts the choice to the modules relevant to the category.

Typical modules per category

Category	Authorised modules (MID Annex II)
MI-001 Water meters	B+F, B+D, H1
MI-002 Gas meters and converters	B+F, B+D, H1
MI-003 Active-energy meters	B+F, B+D, H1
MI-004 Heat meters	B+F, B+D, H1
MI-005 Fuel dispensers and liquid systems	B+F, B+D, H1, G
MI-006 Automatic weighing	B+D, B+E, B+F, D1, F1, G, H1 depending on sub-category
MI-007 Taximeters	B+F, B+D, H1
MI-008 Material measures	A1, F1, D1, B+E, H
MI-009 Dimensional measuring	F1, D1, B+E, B+D, H, H1, G
MI-010 Exhaust-gas analysers	B+F, B+D, H1

For the precise meaning of modules A, A1, B, C, D, D1, E, E1, F, F1, G, H, H1, see the guide to 768/2008 conformity modules. Notified Body intervention is mandatory in virtually all cases; pure module A without variants is not authorised under MID. The choice between B+D, B+F and H1 depends on production volume, quality-system maturity and business model:

B+F: EU-type examination followed by batch verification. Suited to small series or unit production.
B+D: EU-type examination followed by production quality assurance. Suited to stable series, provided a certified QMS is in place.
H1: full quality assurance with design examination. Suited to mature manufacturers certifying several instrument categories.
G: per-unit verification by the Notified Body, reserved for special instruments at very low volume.

Notified Body selection

The Notified Bodies competent for MID are listed in the European Commission NANDO database, with the scope of their designation (MI-00x category and covered modules). See the guide to Notified Body selection via NANDO. A Notified Body designated for MI-001 (water meters) is not automatically competent for MI-003 (electrical meters): the scope of the notification must be verified before any contractual engagement.

The M marking and its format

A MID-compliant instrument carries two complementary markings: the CE marking and the supplementary metrology M marking.

Composition of the M marking

The metrology marking is composed of:

The capital letter M placed inside a rectangle.
The last two digits of the year of affixing (for example "26" for 2026).
The four-digit identification number of the Notified Body that participated in the production-stage conformity assessment (module D, F, H, and so on).

Typical format: CE M26 0123, where 0123 designates the Notified Body. The NB number is the one shown in the NANDO database.

Affixing

The CE marking and the M marking must be affixed in a visible, legible and indelible manner on the instrument itself. Where the nature of the instrument prevents this, they may be affixed on the accompanying documentation and on the packaging, in line with the rules of Annex IV of Decision 768/2008/EC.

For the dimensional and visual rules of the associated CE marking, see the guide to CE marking dimensions and visual rules.

Legal meaning

The M marking attests specific conformity to MID requirements, in addition to the CE marking which attests conformity to the applicable directives in the broader sense. A MID instrument bearing only the CE marking without the M marking is non-compliant and cannot be used for legal-metrology purposes, even if the technical documentation is otherwise complete.

MID versus NAWI: the scope split

Directive 2014/31/EU, known as NAWI (Non-Automatic Weighing Instruments), is the twin of MID, published on the same day, aligned on the same 768/2008 architecture, but reserved to non-automatic weighing instruments.

Criterion	MID 2014/32/EU	NAWI 2014/31/EU
Instrument category	Ten categories MI-001 to MI-010 (water, gas, electricity, heat, fuel, automatic weighing, taximeter, material measures, dimensional, exhaust gas)	Non-automatic weighing only
Key definition	Instrument providing a result automatically	Instrument requiring operator intervention during weighing
Typical modules	B+D, B+F, H1, G	B+D, B+F, G
Marking	CE + M[year][4-digit NB]	CE + M[year][4-digit NB] + green sticker
OIML recommendation	By category (R 49, R 137, R 46, R 75, etc.)	OIML R 76

A weighing instrument is non-automatic when the operator must intervene during the weighing process (reading, positioning, triggering, validating); it is automatic when the cycle proceeds without human intervention between loading and reading. A shop scale is non-automatic (NAWI). An automatic conveyor-belt weighbridge is automatic (MID MI-006).

The boundary turns on absence of operator intervention, not on the presence of electronics or data transmission. An electronic laboratory balance with a digital display remains non-automatic under NAWI as long as an operator places each sample and validates each reading.

Software for measuring instruments: WELMEC 7.2

WELMEC, European Cooperation in Legal Metrology, is the regional organisation that coordinates the national legal-metrology authorities of the Member States. It publishes application guides that are not legally binding but are widely used by Notified Bodies to assess conformity.

Guide 7.2 on software

WELMEC Guide 7.2, titled "Software Guide (Measuring Instruments Directive 2014/32/EU)", is the consolidated European reference for software in MID instruments. It describes:

Software classification: software embedded in a purely metrological instrument, software hosting both metrological and non-metrological functions, separate software for downstream processing.
Software risk class: extension P (protection against modification), extension T (data transmission) and other extensions according to the usage profile.
Metrology stability requirements: separation between legally relevant and non-relevant functions, integrity of stored data, traceability of updates.
Software-sealing requirements: cryptographic signatures, tamper-evident logs, privileged passwords.
Update requirements: authorisation check, image signature, retention of the update log.

A MID instrument whose software does not follow the WELMEC 7.2 doctrine is rarely certified: European Notified Bodies have adopted this guide as their practical reference.

IEC 60050 vocabulary

The vocabulary applied to software and metrology electronics follows the IEC 60050 standard (International Electrotechnical Vocabulary), notably its chapters 300 (measurement), 301 (electrical instruments), 311 (instruments using an electrical signal) and 351 (control technology). The Notified Body expects documentation using this normative vocabulary to avoid terminological ambiguity.

Articulation with cybersecurity

The scope of WELMEC 7.2 and MID covers metrology stability: that the displayed result remains faithful to the physical measurement. It does not cover general cybersecurity under the Cyber Resilience Act (CRA), which will apply to connected instruments for general product-security aspects. The two frameworks are complementary: an MI-003 smart meter will follow WELMEC 7.2 for metrology integrity and the CRA for general cybersecurity.

Verification and market surveillance

Initial verification

Initial verification (first putting into use) is carried out under the chosen assessment module (B+F, B+D, H1, etc.). The M marking is affixed there. The instrument may then be placed in service for legal-metrology use.

Periodic verification

Periodic verification in service is the responsibility of national legal-metrology authorities, which set its frequency by category. This step is not covered by MID itself but by national transpositions (in France, Decree 2001-387 and specific orders). A water meter or electrical meter is verified in service at a frequency set by national regulation.

Market surveillance

National authorities (in France the LNE and DGCCRF coordinate; in Germany the PTB; in the United Kingdom outside the EU, the NMRO) carry out market controls: sampling, metrology checks, control of the M marking and the technical file. Non-compliant instruments may be withdrawn from the market, and the manufacturer or importer exposed to sanctions.

For the cross-cutting surveillance framework, see the market surveillance RAPEX guide.

A communicating active-energy electrical meter (smart meter) accumulates several regulatory frameworks:

MID 2014/32/EU annex MI-003: metrology stability, accuracy, accuracy classes, integrity of the energy count.
RED 2014/53/EU: conformity of the radio part (band used, power, spectrum), where the instrument communicates by radio (RF mesh, cellular).
EMC 2014/30/EU and LVD 2014/35/EU: electromagnetic compatibility and electrical safety for parts not covered by MID.
GDPR (Regulation 2016/679): hourly or sub-hourly load curves are personal data from which behaviour can be inferred; processing requires a legal basis and minimisation measures.
Cyber Resilience Act (CRA): once in application, cyber-security requirements for products with digital elements apply.

Multi-directive conformity assessment requires coordination across the functions of each framework. The M marking attests MID conformity; it says nothing about RED, EMC, GDPR or CRA conformity.

Common pitfalls

Generic CE marking without M marking

The most frequent error: presenting a MID instrument with only the classic CE marking, on the assumption that it is enough. A MID instrument without the M marking is not compliant and cannot be used for legal metrology. The presence of the M marking is essential; its absence is a non-conformity immediately detected by market surveillance.

Wrong MI annex

Confusing MI-00x categories leads to applying the wrong MPE grid and the wrong module grid. A heat meter falls under MI-004, not under MI-003 (active-energy electrical). A gas-volume converter falls under MI-002, complementing the gas meter, not under MI-003. The strict reading of Annex IX and explicit attachment to an MI annex must appear at the head of the technical file.

Software documentation not following WELMEC 7.2

Submitting a MID file whose software is not documented under WELMEC 7.2 practically always leads to refusal or to a request for additional information. Notified Bodies expect software classification, identification of legally relevant functions, documentation of software sealing and the update log. This documentation must be planned from the design stage, not reconstructed at the end of the project.

Own-use versus commercial-use confusion

A manufacturer assumes in good faith that an instrument sold for "internal energy monitoring" escapes MID. If the instrument is later resold to an operator who uses it to bill a sub-tenant or to declare a regulated consumption, it falls retroactively into the MID scope, and the manufacturer must demonstrate conformity. Better to treat MID as soon as a legally relevant use is foreseeable.

MID confused with NAWI

A shop scale is not covered by MID MI-006 (which covers automatic weighing). It falls under NAWI 2014/31/EU. Conversely, an automatic conveyor-belt weighbridge falls under MID MI-006 and not under NAWI. The boundary turns on the presence or absence of operator intervention during weighing. The confusion leads to applying the wrong evaluation grid and to involving a Notified Body not designated for the actual category.

Forgotten periodic verification

The manufacturer and the importer handle initial verification, but periodic verification in service is often forgotten in the chain of responsibilities. It is the operator (distributor, network manager, carrier) that must ensure periodic verification and budget for it. A failure of periodic verification invalidates the legal weight of the measurements made on that basis, with potential consequences on bills issued on that basis.

Metrology components substituted without re-evaluation

Replacing a sensor or an electronic module of a certified meter without informing the Notified Body invalidates the EU-type examination certificate for the new version. The general substitution rule applies, and any substitution of a metrology-bearing component triggers a re-evaluation. See the component substitution rules guide.

Articulation with the glossary and the CE pillar

For cross-cutting definitions (Notified Body, EU declaration of conformity, market surveillance, presumption of conformity, NLF, NANDO, etc.), see the glossary and the CE pillar. For the overview of assessment modules, see the 768/2008 modules guide. For the "self-declaration versus Notified Body" criteria grid, see the self-declaration versus Notified Body guide.