Rules 12 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.
After the seven base units, the National Standards Rules list every other unit that may be used: supplementary and derived units, SI prefixes, units permitted alongside the SI, special and temporarily accepted units, units being phased out, physical constants and coefficients. Rules 12 to 21 say which Schedule governs which class, and the ten Schedules hold the lists.
These rules are as amended up to the Legal Metrology (National Standards) (Amendment) Rules, 2019, which did not change rules 12 to 21 or the Schedules; later amendments should be checked on the Department of Consumer Affairs website. If you need help working out which units your product, instrument or labelling may use, a legal consultation can save a compliance slip.
Supplementary, derived, permitted, special and temporarily accepted units each have their own Schedule; SI prefixes are in the Third Schedule. Units in the Seventh and Eighth Schedules (centimetre-gram-second units and units outside the SI) are not ordinarily to be used except for scientific and technological research, and not ordinarily for education. The Central Government reviews the temporarily accepted units at least once in every ten years (rule 17). No new unit may be formed or used outside research without the Central Government's previous approval (rule 21).
Rules 12 to 21 in plain words
Rule 12: supplementary units
The units in the First Schedule are the supplementary units, each with its symbol. The Schedule has two: the radian (symbol rad) for plane angle and the steradian (symbol sr) for solid angle.
Rule 13: derived units
The units in the Second Schedule are the derived units with their symbols, and no other units may be used for the quantities listed there except for scientific or technological research. The Schedule is arranged in Parts (Part I to Part VII), beginning with units relating to space and time: the square metre for area, the cubic metre for volume, the hertz (Hz) for frequency, the radian per second for angular velocity, the metre per second for speed. Derived units with special names, such as the newton (N), can be used to express other derived units simply.
Rule 14: decimal multiples and sub-multiples
Decimal multiples and sub-multiples of base, supplementary, derived or other units are formed, unless otherwise specified, by using either the full name or the symbol of an SI prefix from the Third Schedule, used in the manner the Schedule specifies.
Rule 15: permitted units
The units in the Fourth Schedule may be used along with the SI units, subject to the limits in the Schedule. The multiples and sub-multiples of time and plane angle units are formed only in the manner the Schedule specifies. The Schedule lists:
- time: the minute (min), the hour (h) and the day (d), with the week, month and year corresponding to the Saka calendar or the Gregorian calendar;
- plane angle: the degree, the minute and the second of arc;
- volume: the litre (l), which is not to be used for work involving precise measurements; and
- mass: the tonne (t), with only the prefixes kilo, mega, giga and tera used with it.
Rule 16: special units
The units in the Fifth Schedule are used so that their values are expressed in SI units or a combination of SI units; multiples and sub-multiples take the SI prefixes in the Third Schedule. They are the electron volt (eV) for energy, the unified atomic mass unit (u) for atomic mass, and the astronomical unit (AU) and the parsec (pc) for stellar distance.
Rule 17: temporarily accepted units
The unit specified in the Sixth Schedule may also be used, on the condition that the Central Government reviews at least once in every ten years from commencement whether it should stay in general use. The review may be taken up earlier on its own motion or on a recommendation of the General Conference on Weights and Measures or the International Organisation of Legal Metrology. The Schedule covers the nautical mile for marine and aerial navigation, the knot, the angstrom for the wavelength of light, and the are (a) and the hectare (ha) for land area; the SI prefixes are not used with the are or hectare.
Rule 18: units to be progressively discontinued
- The centimetre, gram or second units in the Seventh Schedule, and the units outside the SI in the Eighth Schedule, shall not ordinarily be used except for scientific and technological research, and not ordinarily for imparting education (18(1)).
- They are not to be used in any field except scientific and technological research (18(2)).
- When used for research they are used only with the symbols the Schedules specify (18(3)).
The Seventh Schedule is headed centimetre-gram-second units with special names; the Eighth names units such as the fermi, the torr, the kilogram-force, the calorie, the micron, the X unit, the stere and the gamma.
Rule 19: physical constants
The physical constants in the Ninth Schedule, with their numerical values, are used for all purposes except research connected with determining their values.
Rule 20: coefficients
Coefficients include the terms defined in the Tenth Schedule, each with its symbol; ordinarily those coefficients and symbols are used. A corresponding coefficient not in the Schedule may be used for five years from the commencement of the rules, and the same five years apply to a coefficient corresponding to one later added; on expiry, the Schedule's coefficients and symbols become compulsory.
Rule 21: new units
No new unit or weight or measure may be formed or used, except for scientific and technological research, without the previous approval of the Central Government.
Map of the Schedules
| Schedule | Rule | What it lists |
|---|---|---|
| First | 12 | Supplementary units: radian (rad), steradian (sr) |
| Second | 13 | Derived units and symbols, in Parts I to VII, from space and time units onward |
| Third | 14 | SI prefixes and how to use them |
| Fourth | 15 | Permitted units: time, plane angle, volume (litre), mass (tonne) |
| Fifth | 16 | Special units: electron volt, unified atomic mass unit, astronomical unit, parsec |
| Sixth | 17 | Temporarily accepted units: nautical mile, knot, angstrom, are, hectare |
| Seventh | 18 | Centimetre-gram-second units with special names |
| Eighth | 18 | Units outside the SI that are to be phased out |
| Ninth | 19 | Physical constants and their numerical values |
| Tenth | 20 | Coefficients and their symbols |
The Schedules also carry numerical values and conversion factors, which this article does not reproduce. Check the official text for any numerical value or conversion factor before you rely on it.
Who is affected
| Person | Effect |
|---|---|
| Manufacturers, label designers, instrument makers | Use the SI and the permitted units in the Fourth Schedule; avoid the Seventh and Eighth Schedule units |
| Schools, publishers, trainers | Not ordinarily to use discontinued units for education |
| Researchers | May use discontinued units for scientific and technological research, with the Schedule symbols |
| Government | Reviews temporarily accepted units at least once in every ten years; approves new units |
For the Act's section on standard units see sections 7 and 8, and for the first part of these rules see our article on rules 1 to 11.
A practical example
Sunrise Education Press prepares a school physics workbook that quotes pressure in torr and a calorie-based heat problem. Rule 18(1) says the units of the Eighth Schedule are not ordinarily to be used for imparting education, so the editor replaces them with SI units. A research laboratory writing a paper may still use those units, but only with the Schedule's symbols (rule 18(3)). A nautical chart, by contrast, may use the nautical mile and the knot, as they are temporarily accepted units under rule 17.
Common lapses
- Using discontinued units (Seventh and Eighth Schedules) in labels, textbooks or trade documents.
- Using the litre for precise measurement, which the Fourth Schedule rules out.
- Using SI prefixes with the are or hectare, which the Sixth Schedule rules out.
- Inventing a new unit without the Central Government's approval.
For the overview posts see Standard Units of Weights and Measures in India and the Act's sections 4, 5 and 6.
Need help with units and labelling?
If you are unsure whether a unit on your label, price list or instrument is allowed, our team can check it against these rules. Start with a legal consultation.
Key takeaways
- Each class of unit has its own Schedule: First (supplementary), Second (derived), Third (prefixes), Fourth (permitted), Fifth (special), Sixth (temporarily accepted).
- The Seventh and Eighth Schedule units are not ordinarily used outside scientific and technological research.
- Temporarily accepted units are reviewed at least once in every ten years.
- Physical constants in the Ninth Schedule are used for all purposes except research to determine their values.
- Corresponding coefficients not in the Tenth Schedule may be used for five years.
- A new unit needs the Central Government's previous approval, except for research.
Read next
- Rules 1–11: definitions and the seven base units after the 2019 amendment
- Rules 22–33: national prototypes, NPL and reference, secondary and working standards
- Sections 7 and 8 of the Legal Metrology Act, 2009: standard units and standard weights and measures
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.