Quantities and units
Describe a quantity as a numerical value with a unit, and distinguish its physical kind from its dimension. Build length, area, volume and rate units, check meaningful combinations, and separate exact unit relations from measurement uncertainty.
Key knowledge
A physical quantity assigns a magnitude to a property of a phenomenon, body or substance; its value is expressed using a number and a reference, commonly a unit.
Conditions and scope
- This is the metrological meaning of quantity; a nominal label alone is not a quantity value.
Sources · 11
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Bureau International des Poids et Mesures (BIPM)2 sources
- SI Brochure · 9th edition · Version 4.01 (June 2026)Bureau International des Poids et MesuresReference guide · PDF
- International Vocabulary of Metrology (VIM3)Joint Committee for Guides in Metrology (JCGM)Reference guideVIM, 1.1: QuantityVIM, 1.19: Quantity valueVIM, 1.30: Nominal property
- Guide for the Use of the SI · Chapter 7 · Values of quantitiesNational Institute of Standards and TechnologyReference guide
- TIMES Module 10 · Introduction to MeasurementAustralian Mathematical Sciences InstituteTeaching resource
- Grade 10 Physics · Educational Package (2024)Palestinian Ministry of EducationTextbook chapter
- International vocabulary of metrology, third edition (2012)Joint Committee for Guides in Metrology (JCGM)Reference guide · PDF
- A beginner’s guide to uncertainty of measurement · Guide 11, issue 2Stephanie A. Bell, National Physical LaboratoryTeaching resource · PDF
Evidence and review
VIM 1.1 and 1.19: quantity and quantity value.
2026-10-10 · Definition and number/reference distinction only; no claim that every property is quantitatively measurable.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Scope or convention differs
Measurement expresses a property using a numerical value and unit.
This practical guide supplements the fuller metrological definition; it does not classify every nominal property.
National Physical Laboratory
- A beginner’s guide to uncertainty of measurement · Guide 11, issue 2 United KingdomEnglishShared standard
§1.1 What is a measurement?, p.1 (PDF p.10)
- A beginner’s guide to uncertainty of measurement · Guide 11, issue 2
Related articles
Quantities, units and dimensions ↗Entry details
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