Culinary Arts

What's the Difference Between the Metric and Imperial System? Plus a Conversion Chart for Imperial and Metric Systems of Measurement

Written by MasterClass

May 21, 2019 • 3 min read

While most of the world uses the international system of units, aka the metric system, the United States has its own system, based on the old British Imperial System of inches and pounds. This becomes relevant in the kitchen when dealing with international recipes that use grams and Celsius.

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What Is the Metric System?

Based on the meter for length and kilogram for mass, the metric system was first adopted in France in 1795. After the French Revolution, the government asked scientists to look into replacing thousands of different traditional measurement systems with one that could unify the country. The meter was developed by measuring one-ten-millionth of the quadrant of Earth’s circumference running from the North Pole to the equator, through Paris. The new unit, equal to about thirty-nine inches, was called a meter, and all measurements were based upon it.

The metric system, or SI (Système International), is based off this original meter and currently the official system of measurement for almost all countries, including the countries of the former British Empire, such as Australia. (Canada converted to the metric system in the ’70s and ’80s.) The SI units—fundamental units not based on any other units—are meter, kilogram, second, ampere (electricity), Kelvin (although Celsius is a more practical measurement for nonscientific applications), mole (chemistry), and candela (luminous intensity).

What Is the Imperial System?

The British Imperial System was the official system of weights and measures in the United Kingdom from 1824 until they adopted the metric system in 1965. The Imperial system standardized measurements for units like pound and foot that had different meanings in different places. The United States Customary System is based off British Imperial units that existed previous to the Weights and Measures Act of 1824.

How Is the British Imperial System Different From the US System?

There are a few key differences between the US system and the Imperial System used in Great Britain until they adopted the metric system: The US gallon is based on a 231-cubic-inch wine gallon; a US liquid pint is 0.473 cubic decimeter and a dry pint is 0.551 cubic decimeter; and the British stone (equal to 14 pounds) is not used in the US.

Why Doesn't the US Use the Metric System?

Since the United States Customary System was in place during the Industrial Revolution, it’s the measurement system that US manufacturing is based on, and so big business has campaigned against movements to adopt the metric system. Since both the US Customary and metric systems are taught in schools, many Americans feel there’s no need to switch over to metric. Liberia and Myanmar are the only other countries that have not officially adopted the metric system.

Is Cooking With Metric or Imperial Better?

Although not strictly part of the Imperial System, US recipes tend to use cups for units of measurement, while international recipes often use metric measurements, listing ingredients in grams. Measuring out ingredients in grams is more accurate than cups, since the amount of ingredients in a cup can vary depending on how tightly packed your ingredients are. If you bake bread, or use other recipes where precision is important, it’s not a bad idea to invest in a kitchen scale that measures in grams. Teaspoons and tablespoons are handy for smaller measurements, and often used internationally.

How to Convert Metric Units to Imperial Units

VOLUME

  • 1 milliliter = 0.034 US fluid ounces
  • 1 liter = 1 US quart (liquid)

LENGTH

  • 1 meter = 39.37 inches, about 3 feet
  • 1 centimeter = 0.39 inches
  • 1 millimeter = 0.039 inches (to approximate, divide by 25)

AREA

  • 1 square meter = 1.2 square yards, or 10.76 square feet
  • 1 square centimeter = 0.155 square inches

WEIGHT/MASS

  • 1 gram = 0.035 ounces (weight)
  • 1 kilogram = 2.2 pounds

TEMPERATURE

To convert Celsius to Fahrenheit, multiply the temperature in degrees celsius by 9/5, then add 32 (freezing is 0°C and 32°F).

Some common metric conversions for baking are:

130°C = 250°F
150°C = 300°F
190°C = 375°F
200°C = 400°F
230°C = 450°F