U.S. customary units

The US customary system of measurement is based on English units of measurement, the system used in England prior to its replacement by the imperial system.

Customary units definition

US customary units make up a system of units of measurement that is most commonly used inside the US. It was adopted in 1832 and is sometimes referred to as simply the "customary" or "standard" system, or more formally "traditional systems of weights and measures." The customary system systems shares many units of measurement with English units and the imperial system, but many of the units are defined differently.

In 1893, many US customary units were redefined in terms of the meter and kilogram, and in 1959, these definitions were further refined. US customary units are mostly used in everyday life and commercial activities, while SI units are used in many other areas such as science, medicine, industry, the government, and the military. The US has not officially adopted The International System of Units (SI) as a country, but SI is relatively widely used outside of everyday contexts.

The US customary system includes units for measuring length, weight, capacity, area, volume, and temperature.

Customary units of length

US customary units of length include inches (in), feet (ft), yards (yd), and miles (mi).

• 1 ft = 12 in


• 1 yd = 3 ft = 36 in
  
  
• 1 mi = 1760 yd = 5280 ft

The various units of length are used for different purposes:

• Inch: used to measure small lengths such as a phone screen size.


• Feet: used to measure small-medium lengths such as the height of a ladder.


• Yard: used to measure large distances like the length of a football field.


• Mile: used to measure very large distances such as the distance between two cities.

Customary units of weight

Commonly used units for measuring weight in the US customary system include ounce (oz), pound (lb), and ton (T).

• 1 lb = 16 oz


• 1 T = 2000 lbs

The various units of weight are used for different purposes:

• Ounce: used to measure small weights such as a cut of steak.


• Pound: used to measure medium a large range of weights, most commonly body weight.


• Ton: used to measure large weights such as cars.

Customary units of capacity

Commonly used units for measuring capacity in the US customary system include teaspoons (t), tablespoons (T), cups (C), pints (pt), quarts (qt), and gallons (gal). These measures are typically used for measuring fluids. Capacity is slightly differentiated from volume; capacity is the amount of fluid a container can hold while volume is the amount of space an object takes up.

• 1 tablespoon = 3 teaspoons


• 1 cup = 16 tablespoons


• 1 pint = 2 cups


• 1 quart = 2 pints


• 1 gallon = 4 quarts

Fluid ounces (fl oz) are also used for measuring capacity.

• 1 fl oz = 2 tablespoons


• 1 cup = 8 fl oz


• 1 pt = 16 fl oz


• 1 qt = 32 fl oz

The various measures of capacity are used for different purposes.

• Teaspoons, tablespoons, cups: used for the smallest measures of capacity, such as measurements when baking.


• Cups, pints, quarts: used for medium measures of capacity such as amounts of soup or ice cream.


• Gallons: used for larger measures of capacity such as containers of milk or gasoline.


• Fluid ounces: a generic measure of capacity used for many different purposes such as drink or bottle sizes.

Customary units of volume

Cubic units are used for measuring volume. In the US customary system these include in³, ft³, and yd³.

• 1 ft³ = 1,728 in³


• 1 yd³ = 27 ft³ = 46,656 in³

Units of volume are used based on the size of the object in a manner similar to their corresponding units of length.

• Cubic inch: used to measure volumes such as a car gas tank.


• Cubic foot: used to measure medium volumes such as the size of a refrigerator.


• Cubic yard: used to measure large volumes such as construction materials like concrete.

Customary units of area

Square units are used for measuring area. In the US customary system, these include in², ft², and yd².

• 1 ft² = 144 in²


• 1 yd² = 9 ft²

Acres and mi² are also used for measuring large areas.

• 1 acre = 43,560 ft²


• 640 acres = 1 mi²

The various measures of area are used for different purposes:

• Square foot: used to measure area such as apartment size.


• Square yard: used to measure large areas such as football fields.


• Acre, mi²: used to measure sizeable areas such as tracts of land.

Customary units of temperature

The Fahrenheit (°F) scale is used for measuring temperature in the US customary system. Two reference points for this temperature scale are:

• 32 °F: the freezing point of water


• 212 °F: the boiling point of water