Definition
The metre (also spelled "meter" in American English) is the base unit of length in the metric system of weights and measures. Historically defined as the ten-millionth part of the distance from the equator to the North Pole along a meridian, it is equivalent to approximately 39.37 inches, or just over three feet. All other metric units of length — and, by derivation, units of area, volume, and certain units of weight — are defined in relation to the metre through decimal multiples and fractions (e.g., kilometre, centimetre, millimetre).
In legal contexts, the metre appears primarily in statutes, regulations, and contracts that adopt or reference the metric system, as well as in weights-and-measures law governing trade, commerce, and scientific standards.
Common Language
Modern common usage (Wiktionary): Alternative spelling of "meter."
Historical common usage (Webster's 1913): See "Meter." (The 1913 dictionary treats the two spellings as interchangeable, with "meter" as the primary American form.)
The spelling distinction carries no legal significance in itself, but it can signal jurisdictional provenance in documents and statutes. "Metre" is the standard spelling in British, Commonwealth, and international legal instruments (including SI treaty texts), while "meter" predominates in American legislation and regulation. A researcher reading an older Commonwealth statute or an international trade agreement should expect "metre"; an American federal regulation will almost always use "meter." Neither spelling alters the unit's definition.
Common Confusion
METRE (unit of length) vs. METER (measuring device): In American English, "meter" serves double duty — it denotes both the unit of length and any measuring instrument (gas meter, parking meter). "Metre" unambiguously refers only to the unit of length. British and international legal drafting uses "metre" precisely to avoid this ambiguity. In older American legal texts, context is necessary to determine which meaning is intended.
Why It Matters in Research
The metre is not a term of art in the way most dictionary headwords are, but it carries specific technical and jurisdictional significance in legal research.
Metric adoption history: The metric system was first adopted in France in 1795. Its legal status in other jurisdictions arrived in stages. In the United States, metric weights and measures were authorized but not mandated by federal statute beginning in the nineteenth century. Researchers working with American commercial or regulatory documents from different eras will find inconsistent use of metric and imperial units; the governing standard depends on the date and subject matter of the instrument.
Weights-and-measures statutes: Definitions of "metre" or "meter" in domestic law are creatures of statute. The defined value has changed over time as scientific standards evolved — the original meridian-based definition was eventually replaced by physical artifact standards, and later by definitions based on the speed of light under the International System of Units (SI). Legal instruments that incorporate the metric system by reference may import whichever definition was current at the time of enactment, which can matter in highly precise scientific, pharmaceutical, or technical regulatory contexts.
International instruments: Treaties and international commercial agreements routinely use metric units. Researchers analyzing cross-border contracts, customs regulations, or international standards should be alert to whether a document uses the spelling "metre" or "meter" as a soft indicator of which legal tradition governs the drafting.
Corpus connections: In the Law Mind corpus, metre appears most frequently in the context of weights-and-measures law, metrication statutes, international trade regulation, and scientific or pharmaceutical regulatory frameworks. It is also encountered in older property descriptions in jurisdictions that adopted metric land measurement.
Historical Dictionary Support
Both editions of Black's Law Dictionary define the metre consistently as the foundational unit of the metric system and peg its value to the ten-millionth part of the meridional distance from equator to North Pole, equivalent to 39.37 inches. The first edition adds the useful historical note that the metric system was first adopted in France in 1795 and explains the derivative relationship between the metre and all other metric units of measure. The second edition's entry is truncated in the available text but follows the same framing.
Neither edition addresses the subsequent redefinition of the metre under modern SI standards, nor do they discuss American metrication legislation or the distinction between "metre" and "meter" as spelling variants with jurisdictional implications. For research purposes, both entries reflect the state of the law as of their respective publication dates and should not be read as authoritative statements of the metre's current legal or scientific definition.
Jurisdictional Note
"Metre" is the spelling mandated by the International Bureau of Weights and Measures and used in British, Commonwealth, and EU legal instruments. American federal law uses "meter." The underlying unit is identical across jurisdictions, but researchers should use the jurisdiction-appropriate spelling when searching statutory and regulatory databases to avoid missed results.