Measuring things allows us to describe the world in numbers. A measurement system determines characteristics such as size, length and distance, mass and weight as well as volume.

The metric system is widely adopted in the world and is therefore nearly universal. However, due to the reach of the English language, the imperial systems of Great Britain and the United States and their units of measurement are also well known, though they’re only in use in very few countries. We’ll look at the differences between the metric system vs the imperial system.

Key facts: metric system vs imperial system

What is the metric system?

The metric system is also called the International System of Units, Système International or SI for short. This measurement system has official status in nearly every country in the world. All but three countries have adopted the metric system.

The metric system is a decimal system: it uses decimal multiples to systematically construct a set of units of the same physical quantity. For example: the metre is a coherent unit of length, consisting of 100 centimetres. One thousand metres make up one kilometre. The metric prefix kilo signified for the factor of 1,000, while the prefix centi stands for the factor of 100. The conversion from one unit to another is always through a power of ten.

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The metric system has seven base units: the second, the unit of time with the symbols, the metre for length with the symbol m, the kilogram for mass with the symbol kg, the ampere for electric current with the symbol a, kelvin for thermodynamic temperature with the symbol K, mole for the amount of substance with the symbol mol and candela for luminous intensity with the symbol cd.

Additional units are possible as derived units. The metric system currently uses twenty-two derived units with special names and symbols.

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What is the imperial system?

The imperial system is a system of measurements consisting of units such as the inch, the mile and the pound. The British Imperial System was developed as a unifying, single measurement system for use in the United Kingdom and other Commonwealth countries. The United States Customary System or USCS is based on the British Imperial System, which is why the term imperial system or IS for short is still used today to describe both systems of measurement.

Only three countries in the world use the imperial system of measurement: the United States of America, Myanmar and Liberia. It’s worth noting that despite the lack of universal adoption, the United States and the United Kingdom recognise the metric system with an official status.

The units of measure of the imperial system trace back to Ancient Roman units. The units of length use the yard as their base. Today, the international yard is defined as exactly 0.9144 metres. Other linear measure units are the inch, foot and mile, as well as chain and furlong. The US system also knows the survey measures link, survey foot, rod, pole or perch, and the US Statute mile. Areas are measured in squared units, with the additional units of acre, which is equivalent to 4840 square yards, the rood in the UK and the township in the US.

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Units of dry volume are the cubic inch, foot and yard, while the US also uses the bushel and dry print, quart and peck. Liquids are measured in units such as the gallon, quart, pint or fluid ounce. Weights are based on the Avoirdupois system using grain, dram, ounce, pound and the ton, which the US defines as 2,000 pounds while the UK defines it as 2240 pounds.

Comparison: metric system vs imperial system

Overview

Here is a quick comparison overview of the names and sizes for fundamental units the two different systems of measurement use.

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Differences

As we’ve outlined above, the metric system is based on the meter as the unit of measurement, which is derived from the circumference of the earth. In this decimal system, unit conversion is straightforward: you divide or multiply by powers of ten. In the imperial system, you don’t have an easy way for converting units.

Many people argue that the metric system is superior to the imperial system due to easier conversion and widespread adoption. It is a de facto and (near) universal standard the world over and easy to use because all units of measurement relate to each other.

Today, the US also teaches the metric system in schools and modern measurement tools often include units in both the international system and the imperial system. US products packaged for the international market show quantities listing both units. However, adopting the metric system in the United States of America would require a massive infrastructure change, a costly effort likely to take up decades.

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Conversion: from metric system to imperial

The following table will help you convert between units from the metric system and the imperial system.

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