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international system of units

Medium-low
UK/ˌɪn.təˌnæʃ.ən.əl ˌsɪs.təm əv ˈjuː.nɪts/US/ˌɪn.t̬ɚˈnæʃ.ən.əl ˌsɪs.təm əv ˈjuː.nɪts/

Formal, Academic, Technical

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Definition

Meaning

The modern, standard form of the metric system, defining seven base units (metre, kilogram, second, ampere, kelvin, mole, candela) from which all other measurement units are derived.

The globally coherent system of measurement units, established and maintained by the General Conference on Weights and Measures (CGPM). It is the world's most widely used measurement system in science, technology, industry, and commerce.

Linguistics

Semantic Notes

Always capitalised. Often abbreviated as 'SI' (from French 'Système International'). Represents a specific, codified system, not just any system used internationally.

Dialectal Variation

British vs American Usage

Differences

No significant differences in meaning or usage. The abbreviation 'SI' is universal in technical contexts. British English may occasionally use the full French term 'Système International (d'Unités)' in historical or formal contexts.

Connotations

Connotes scientific rigour, standardisation, and global cooperation. No regional connotative differences.

Frequency

Equally low-frequency in general discourse but high-frequency in scientific, engineering, and educational (STEM) contexts in both regions.

Vocabulary

Collocations

strong
SI unitsbase unitsadopt the International System of UnitsSI prefixcoherent system
medium
defined by the International System of Unitsmeasurement in the International System of Unitsstandardised by the International System of Units
weak
global systemmetric frameworkscientific standards

Grammar

Valency Patterns

[The] International System of Units + verb (defines, establishes, uses)[Measurement] + in + the International System of Units[To adopt/use/apply] + the International System of Units

Vocabulary

Synonyms

Strong

Système International

Neutral

SImetric system (in its modern form)

Weak

modern metric systemglobal measurement standard

Vocabulary

Antonyms

imperial systemUS customary unitsnon-standard units

Phrases

Idioms & Phrases

  • “Speak SI (jargon: to use SI units consistently)”

Usage

Context Usage

Business

Used in international trade specifications, product labelling (e.g., weight in kg), and technical documentation to ensure clarity.

Academic

Fundamental in all natural sciences, engineering, and medicine for reporting data and calculations. The mandatory system in scientific publishing.

Everyday

Rarely used as a full term; laypeople encounter 'metric units' (litres, metres, grams) without referencing the overarching system.

Technical

The precise, formal reference for all standardized measurements. Critical for calibration, metrology, and interoperability in technology and research.

Examples

By Part of Speech

verb

British English

  • The laboratory will SI-tise all its measurement protocols by next year. (informal/jargon)

American English

  • The manufacturer decided to SI-ify their technical manuals for the global market. (informal/jargon)

adverb

British English

  • The data was presented SI-consistently throughout the paper. (jargon)

American English

  • The apparatus was calibrated SI-compliantly. (jargon)

adjective

British English

  • The SI unit for luminous intensity is the candela.
  • Follow the SI conventions for unit symbols.

American English

  • An SI measurement was required for the international project.
  • The report used standard SI prefixes like kilo- and milli-.

Examples

By CEFR Level

A2
  • We use kilograms and metres. They are part of the International System of Units.
B1
  • In science class, we learn to measure using the International System of Units, like metres for length and litres for volume.
B2
  • The International System of Units provides a coherent framework for measurement, ensuring that a newton is always a kilogram metre per second squared.
C1
  • The redefinition of the kilogram in 2019, based on Planck's constant, marked a historic shift for the International System of Units towards constants of nature.

Learning

Memory Aids

Mnemonic

SI Simply Includes: Second, Metre, Kilogram, Ampere, Kelvin, Mole, Candela (the seven base units).

Conceptual Metaphor

A UNIVERSAL LANGUAGE (of measurement); a FOUNDATION (for science and trade).

Watch out

Common Pitfalls

Translation Traps (for Russian speakers)

  • Do not translate as 'международная система измерений' in precise contexts—the standard term is 'Международная система единиц (СИ)'.
  • The abbreviation 'SI' is used identically in Russian ('СИ'), avoid translating it back to English as 'CI'.

Common Mistakes

  • Incorrect: 'international system of unit' (missing plural 's').
  • Incorrect: Using lowercase for 'International System of Units' in formal writing.
  • Incorrect: Confusing SI (the coherent system) with the broader, historical 'metric system' which included non-SI units like the calorie.

Practice

Quiz

Fill in the gap
For global consistency in scientific papers, all measurements must be reported using the .
Multiple Choice

What does the 'SI' in 'SI units' stand for?

FAQ

Frequently Asked Questions

The SI is the modern, coherent form of the metric system. The broader term 'metric system' can historically include some non-SI units, but in contemporary scientific and technical use, they are synonymous.

Because it standardises the specific 'units' of measurement (metre, second, etc.), not the act of measuring itself. It's a system of defined, interrelated units.

There are seven base units: metre (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity).

Yes, both countries have officially adopted the SI as their primary system for science, medicine, and many aspects of trade and government. However, in everyday life, the US continues widespread use of US customary units alongside SI.