What is the Imperial System?

The imperial system is a measurement system originating from the UK and defined in the British Weights and Measurements Act of 1824. The imperial system uses measurements such as the inch, foot, pound, and gallon.

What is the Imperial System?

The imperial system and the United States Customary Units systems are similar. Although, the United States made some changes after it gained independence from Britain.

History of the Imperial System

Before the introduction of the imperial system, Britain used many of the same measurements as defined in the imperial system, although these measurements varied by location, time, and product. It was in the 10th century when weights and measures first went through standardization, as then Saxon King Edward the Peaceable defined the “bushel.” The Royals gave the measurements the name of “Winchester Standard.”

Up through the 15th century, more leaders defined measurements, adding them to the Winchester Standard. These included the yard, foot, and inches, as well as measurements for capacity. The royals distributed these standards throughout the kingdom to create uniformity.

During the Elizabethan age, more weights and measurements were standardized, including the rod, acre, furlong, troy pound, and avoirdupois.

The British Weights and Measures Act of 1824 and 1878 created the imperial system, basing a uniform standard of measurements on units defined in the Winchester Standard. While the act has gone through amendments, today’s imperial units originated from this act.

Great Britain began to switch to the metric system, a unified measuring system based on the power of ten, in 1965. Today, much of the UK uses a combination of imperial and metric system units.

Imperial System Units

The imperial system assigns length, weight, volume, and area measurements. 

Here’s a look at the most common imperial system units.

Unit NameAbbreviationMeasurement Type
Square inchessq. in.area
Square feetsq. ft.area
Square milesq. mi.area
Fluid ouncefl. oz.volume

Unlike the metric system, the imperial measurement system doesn’t use decimals, so conversions are difficult. 

In the metric system, it’s easy to remember that a centimeter is 1/100th of a meter and a kilometer is 1,000 meters – everything is based on powers of ten. But more complex calculations are needed for the imperial system, which can be hard to memorize. For example, there are 12 inches in one foot, 3 feet in one yard, and 1,760 yards in one mile. 

Common Imperial System to Metric System Conversions

Here’s a look at how some of the most common imperial units convert to metric units.

Imperial UnitMetric Unit Equivalent
1 inch2.54 centimeters
1 foot0.3048 meters
1 mile1,609.34 meters
1 pound 0.453592 kilograms
1 stone6.35029 kilograms
1 gallon0.00378541 cubic meters
1 acre4046.86 square meters

How is the Imperial System Different from the United States Customary Units Systems?

While the imperial and United States Customary systems are both based on English measurements, there are slight differences in the volume measures. For example, the fluid ounce is smaller in the imperial system, while the pint, quart, and gallon are larger.

Another difference is the two systems don’t always share common measurements. For instance, the imperial system doesn’t use the cup for volume measurements, while the US Customary system doesn’t use the stone to measure weight.

Countries that Use the Imperial System

The two countries that use only the imperial system include Liberia and Myanmar. The UK and Canada use a combination of metric and imperial units. The US relies on the United States Customary units, similar to imperial units.