Why Does the World Use Different Measurement Systems?

July 24, 2025 • 5 min read

Only three countries have not officially adopted the metric system: the United States, Myanmar, and Liberia. Yet even in metric countries, people still use "informal" imperial measurements. Why is the world so divided on something as fundamental as how we measure things?

A Brief History

Before standardisation, measurements were based on the human body and local customs:

• ▶ Foot: Literally the length of a human foot (varied by region)
• ▶ Yard: Distance from King Henry I's nose to his outstretched thumb
• ▶ Inch: Width of a thumb, or three barleycorns laid end to end
• ▶ Mile: 1,000 Roman paces (mille passus)

Every town, trade, and country had slightly different definitions. Commerce was chaotic.

The Metric Revolution

In 1799, France created the metric system during the French Revolution. The goals were radical simplicity:

• ▶ Base everything on powers of 10
• ▶ Define units from nature (the metre was 1/10,000,000 of the distance from the equator to the North Pole)
• ▶ Make a universal system free from royal or national bias

Over the next 200 years, nearly every nation adopted it — the "Système International d'Unités" (SI) became the global standard for science, trade, and daily life.

Why the US Never Fully Switched

• ▶ 1975: The Metric Conversion Act was passed — but it was voluntary
• ▶ Cost: Replacing every road sign, ruler, and toolset is expensive
• ▶ Cultural inertia: Generations grew up with feet, pounds, and Fahrenheit
• ▶ No external pressure: As the world's largest economy, the US could trade on its own terms
• ▶ Industry resistance: Manufacturing and construction had too much invested in imperial tooling

However, US science, medicine, military, and many industries do use metric internally.

The UK: Officially Metric, Culturally Imperial

Britain adopted metric in 1965 but still uses:

• ▶ Miles and mph for road distances and speed
• ▶ Pints for beer and milk
• ▶ Stones and pounds for body weight
• ▶ Feet and inches for height

Yet schools teach metric, science uses SI, and food is sold in grams and litres. It is a genuine dual-system country.

The Cost of Confusion

Mixed units have caused real disasters:

• ▶ 1999 Mars Climate Orbiter: Crashed because one team used metric and another used imperial — a $327 million mistake
• ▶ 1983 Air Canada "Gimli Glider": Ran out of fuel because ground crew calculated in pounds but the plane used kilograms
• ▶ Medical errors: Drug dosing mistakes from confusing mg/kg with mg/lb continue to occur

Will We Ever Have One System?

Probably not in our lifetimes. The practical reality is that both systems are deeply embedded in different cultures, industries, and infrastructure. The best we can do is be fluent in both — and use a reliable converter when switching between them.