Rules explained: this guide covers what it means, who it applies to, the step-by-step process, documents required, fees, due dates and penalties in India — so you can stay compliant with confidence and avoid costly mistakes.
The first eleven rules of the National Standards Rules say what the key terms mean, require every unit of weight or measure to be based on the metric system, name the seven base units and, since the 2019 amendment, define each base unit through a fixed numerical value of a natural constant. This article covers the definitions, rule 3 and the base units in rules 4 to 10.
These rules are as amended up to the Legal Metrology (National Standards) (Amendment) Rules, 2019 (G.S.R. 474(E), 5th July, 2019); later amendments should be checked on the Department of Consumer Affairs website. If you need a view on which units your labels, instruments or contracts must use, a legal consultation is a good starting point.
Every unit of weight or measure must be based on the metric system: the International System of Units (SI) recommended by the General Conference on Weights and Measures, plus any additional units recommended by the International Organisation of Legal Metrology (rule 3). The seven base units are the metre, kilogram, second, ampere, kelvin, candela and mole. Rules 4 to 10 were substituted in 2019 so that each is defined by a fixed value of a constant. The word "weight" in the rules is construed as mass (rule 11).
Rule 1: title and commencement
S.O. 211(E), dated the 31st January, 2011, made the Legal Metrology (National Standards) Rules, 2011 under section 52 of the Legal Metrology Act, 2009. They came into force on the 1st day of April, 2011 (rule 1(2)). The rules have four chapters and ten Schedules. For the Act's side, see our post on sections 4, 5 and 6.
Rule 2: definitions (a) to (p)
| Term | What the rules say (in brief) |
|---|---|
| Act | The Legal Metrology Act, 2009 |
| Co-efficient | Parameters without physical dimension, or ratios of quantities of the same kind, needed for particular measurements or to describe properties of substances; for example, degree of alcoholic strength, percentage of sugar and hardness of materials |
| Derived units | Units expressed algebraically in terms of base units, or base and supplementary units, by multiplication or division or both; derived units with special names, such as the newton with symbol N, can express other derived units more simply; dimensionless quantities are expressed by numbers |
| General Conference on Weights and Measures | The conference established under the Metre Convention, to which India acceded |
| International Bureau of Weights and Measures | The Bureau established under the Convention of the Metre, at Sevres in France |
| International Organisation of Legal Metrology | The organisation established under the convention that set it up, to which India acceded |
| International prototype of the kilogram | The prototype sanctioned by the first General Conference and deposited at the International Bureau |
| International System of Units (SI) | The system established by the General Conference, divided into base units, derived units and supplementary units |
| Permitted units | Units not part of the SI but recognised and permitted by the General Conference for general use along with SI units |
| Physical constants | Constants expressing the value of a physical invariant in a given system of units: those linking physical quantities independent of material, those linking microscopic properties of particles, conversion factors, and those describing material properties of pure substances |
| Schedule | A Schedule appended to the rules |
| SI prefix | The name and symbol of a prefix used to form decimal multiples and sub-multiples of SI units and other permitted units |
| Special units | Units outside the SI used in specialised scientific research, whose SI values can be obtained only by experiment and are not known exactly; the electron volt is the example |
| Supplementary units | Units specified as such by the General Conference; they may be used to form derived units |
| Symbol | A letter or group of letters written or combined in the specified manner to represent a unit |
| Temporarily accepted units | Units recognised for the time being by the General Conference for use along with SI units |
For the Schedules and later rules that use these terms, see our article on rules 12 to 21.
Rule 3: the metric basis
Under rule 3(1), every unit of weight or measure is based on the units of the metric system. Rule 3(2) says that the metric system for this purpose means (a) the International System of Units as recommended by the General Conference on Weights and Measures, and (b) such additional units as the International Organisation of Legal Metrology may recommend. Trade, labels and invoices therefore use metric units, which also ties in with the units rule for packages in our post on rule 13 of the Packaged Commodities Rules.
Rules 4 to 10: the seven base units (as substituted in 2019)
G.S.R. 474(E) substituted rules 4 to 10 with definitions that fix the numerical value of a constant. The 2011 text defined the metre, kilogram, second, ampere, kelvin, candela and mole in older ways (a wavelength of krypton-86, the international prototype of the kilogram, the triple point of water and so on); that is history now.
| Rule | Quantity | Base unit | Symbol | Defining constant | Fixed value |
|---|---|---|---|---|---|
| 4 | Length | metre | m | speed of light in vacuum, c | 299792458 metres per second |
| 5 | Mass | kilogram | kg | Planck constant, h | 6.62607015 x 10^-34 J s |
| 6 | Time | second | s | caesium frequency (unperturbed ground-state hyperfine transition frequency of the caesium-133 atom) | 9192631770 Hz |
| 7 | Electric current | ampere | A | elementary charge, e | 1.602176634 x 10^-19 C |
| 8 | Thermodynamic temperature | kelvin | K | Boltzmann constant, k | 1.380649 x 10^-23 J/K |
| 9 | Luminous intensity | candela | cd | luminous efficacy of monochromatic radiation of frequency 540 x 10^12 Hz | 683 lm/W |
| 10 | Amount of substance | mole | mol | Avogadro constant (the Avogadro number of elementary entities) | exactly 6.02214076 x 10^23 elementary entities |
Points to note in each rule
- Rule 4 (metre): defined by the fixed value of the speed of light, with the second defined in terms of the caesium frequency.
- Rule 5 (kilogram): defined by the Planck constant, with the metre and the second defined in terms of the speed of light and the caesium frequency.
- Rule 6 (second): defined by the caesium-133 frequency.
- Rule 7 (ampere): defined by the elementary charge, with the second defined by the caesium frequency.
- Rule 8 (kelvin): defined by the Boltzmann constant. The kelvin is also used for temperature intervals or differences; zero degree Celsius corresponds to 273.15 kelvin; the degree Celsius may also express an interval or difference, a degree Celsius being equal to a kelvin.
- Rule 9 (candela): defined by the luminous efficacy of monochromatic radiation of frequency 540 x 10^12 Hz, in a given direction.
- Rule 10 (mole): one mole contains exactly 6.02214076 x 10^23 elementary entities, a number called the Avogadro number. When the mole is used, the elementary entities shall invariably be specified; they may be atoms, molecules, ions, electrons, other particles or specified groups of such particles.
The 2019 amendment came into force on the date of its publication in the Official Gazette, with no transition period printed in the rules.
Rule 11: weight means mass
Wherever the rules use the expression "weight" as symbolising the quantity of matter, it is construed as representing mass.
Who is affected
| Person | Effect |
|---|---|
| Manufacturers of weights, measures and instruments | Instruments must be based on the metric units |
| Calibration and test laboratories | Work from the SI base units as redefined; see the national standards chapter in our article on rules 22 to 33 |
| Teachers and students | Use the 2019 definitions rather than older textbook ones |
| Compliance staff | Use metric units in labels, invoices and contracts |
A practical example
Precision Mass Labs, a calibration firm, updates its training manual after a new trainee quotes the kilogram as "the mass of the international prototype". The manual now reads: the kilogram is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015 x 10^-34 when expressed in J s. The manual also notes that rules 22(1), 24(4) and 25 still speak of a "national prototype of the kilogram", because the 2019 amendment did not touch them.
Common lapses
- Quoting the 2011 definitions (krypton-86 wavelength, triple point of water) as current.
- Treating "weight" in the rules as a force rather than mass.
- Mixing up the Celsius interval with the kelvin: a degree Celsius equals a kelvin for intervals, and zero degree Celsius corresponds to 273.15 kelvin.
- Forgetting that for the mole the elementary entities must be specified.
For the thinner overview posts see Legal Metrology (National Standards) Rules 2011 and Base Units and Derived Units Under Legal Metrology.
Need help with units on labels and contracts?
If you are checking that your product labels, instrument markings or contracts use the right metric units, our team can help. Start with a legal consultation.
Key takeaways
- The rules came into force on the 1st day of April, 2011.
- Every unit of weight or measure is based on the metric system: the SI and units the International Organisation of Legal Metrology recommends.
- Rules 4 to 10 were substituted in 2019; each base unit is now defined by a fixed value of a constant.
- Zero degree Celsius corresponds to 273.15 kelvin.
- "Weight" in the rules means mass.
- Rules 22(1), 24(4) and 25 still refer to a national prototype of the kilogram; the 2019 amendment did not change them.
Read next
- Rules 12–21: derived, permitted, special and discontinued units and the ten Schedules
- Rules 22–33: national prototypes, NPL and reference, secondary and working standards
- Sections 4, 5 and 6 of the Legal Metrology Act, 2009: metric system, base units and numeration
Disclaimer: Based on the Legal Metrology (Approval of Models) Rules, 2011 (as amended in 2019), the Legal Metrology (Government Approved Test Centre) Rules, 2013 (as amended up to 17 June 2026), the Legal Metrology (National Standards) Rules, 2011 (as amended in 2019), the Legal Metrology (Numeration) Rules, 2011 and the Indian Institute of Legal Metrology Rules, 2011, as published in the Gazette of India and consulted on 4 October 2026. Later amendments, current fees and the Legal Metrology Act, 2009 provisions referred to should be checked on the Department of Consumer Affairs website. This article is general information, not legal advice; check the official text before acting.