Metric vs Imperial: Which Countries Use Which and Why
Discover which countries use metric vs imperial units, why the US never fully converted, and how the two systems compare across everyday measurements.
Of the 195 recognized countries in the world, only three have not officially adopted the metric system as their primary system of measurement: the United States, Myanmar (Burma), and Liberia. The rest of the world โ 192 countries โ uses the International System of Units (SI), the modern form of the metric system, for science, trade, education, and everyday life. Even the United States uses metric in pharmaceutical, military, and scientific applications, making the country effectively a dual-system nation.
A Brief History of Both Systems
The metric system was created in France during the 1790s as a rational, base-10 system intended to replace the chaotic variety of local measurement systems across Europe. By 1875, 17 countries signed the Metre Convention, establishing international standards. The imperial system, used in Britain and its colonies, evolved from older English units and was formally defined by the UK Weights and Measures Act of 1824. Britain itself completed its official transition to metric in 1995, though road signs still use miles.
- 1875: Metre Convention signed by 17 nations in Paris
- 1965: UK begins voluntary metrication
- 1975: US Metric Conversion Act passes โ voluntary, largely fails
- 1995: UK formally adopts metric for trade; road signs remain imperial
Why the United States Never Fully Converted
The United States came close to converting twice. Thomas Jefferson proposed a decimal measurement system in 1790, and Congress nearly adopted metric in 1866 when the Metric Act made metric legal (but not mandatory). The 1975 Metric Conversion Act created the US Metric Board, but President Ronald Reagan disbanded it in 1982. Economists estimate that US industry spends an estimated 300 to 500 million dollars annually on conversion errors and dual-system maintenance, though hard figures remain disputed.
The 1999 Mars Climate Orbiter loss โ valued at 327 million dollars โ was directly caused by a metric-imperial mismatch: Lockheed Martin sent thruster data in pound-force seconds while NASA expected newton-seconds.
Head-to-Head: Metric vs Imperial in Daily Life
Distance: most of the world measures road distances in kilometers (1 km = 0.621 miles). The US, UK, and a few Caribbean territories use miles. Speed limits are in mph in the US, UK, and a handful of others; the rest of the world uses km/h. Weight: grocery stores in Canada, Australia, and Europe sell produce in kilograms. US stores use pounds. A standard bag of flour in Europe is 1 kg (2.2 lb); in the US it is commonly sold as 5 lb (2.27 kg).
Temperature: US weather apps display Fahrenheit, while the rest of the world uses Celsius. Volume: US recipes use cups, tablespoons, and fluid ounces; European recipes use grams and milliliters โ a difference that causes consistent confusion when cooking across national recipe sites, since volumetric measurements of dense ingredients like flour can vary by 20 percent depending on packing.
Advantages of the Metric System
The metric system is designed around powers of 10, which makes calculations error-free by comparison to imperial. Converting 5 kilometers to meters requires multiplying by 1,000. Converting 5 miles to feet requires knowing that 1 mile equals 5,280 feet โ a non-obvious number with no mathematical logic behind it. According to a 2014 study published in Science Education journal, students in metric-primary countries solve unit conversion problems on average 30 percent faster with fewer errors than students in imperial-primary countries.
- Metric multipliers: milli (0.001), centi (0.01), kilo (1,000), mega (1,000,000)
- No base conversion needed: 1 L of water = 1 kg of water = 1,000 mL = 1,000 cm3
- Imperial base units are arbitrary: 12 inches to a foot, 3 feet to a yard, 5,280 feet to a mile
- All 192 metric nations share one system; imperial has US and UK variants that differ (gallons, fluid ounces)
Conclusion
Only the United States, Myanmar, and Liberia have not officially adopted the metric system as their primary measurement standard. The US uses a dual system in practice, with metric standard in science, medicine, and the military. The metric system dominates because its base-10 structure eliminates the arbitrary conversion factors embedded in imperial units. For anyone working across borders โ in trade, science, engineering, or cooking โ understanding both systems and their conversion factors is an essential life skill.