US Standard Units|Definition & Meaning

Figure 1 shows all the US units along with the physical quantities that they belong to.

Figure 1 – US Standard Units for Fluid Volumes, Mass, Length, and Temperature

History

The US standard units were derived and adapted from the imperial system of weights and measures in 1832 by the US government. The imperial system was developed by the British in 1824. Later on, in 1864, the British adopted the metric system, which was developed by French scientists in 1795. but the US still uses its customary units such as pounds, ounces, feet, inches, miles, etc.

All the US standard units are exactly the same as the units of mass, length, etc., used in the imperial system except for the units of volume. The units used to measure the volume of fluids in the US system are smaller than their imperial counterparts. For example, one fluid ounce in the US system is equal to 1.0408 fluid ounces in the imperial system. Also, the US gallon is 20% smaller than the imperial gallon.

The US standard units used to measure the volume of liquids, the mass of dry ingredients, length, and temperature are discussed below.

Volume of Liquids

A liquid is a fluid that takes the shape of its container. It is incompressible and has a constant volume. It is one of the four basic states of matter, having no fixed shape but a definite volume. The volume of liquids is measured in the following US standard units.

Fluid Ounces

The fluid ounce is the smallest unit to measure the volume of a liquid. It is abbreviated as “fl oz” and is also called a regular ounce. The SI volume unit is a cubic meter which is equal to one kiloliter (kL). The smaller unit milliliter (mL) is related to one fl oz as:

1 US fl oz = 29.5735 mL

The US customary fluid ounce is 4.08% greater than the imperial fluid ounce. So,

1 imp fl oz = 0.96076 US fl oz

A fluid ounce is equal to 6 US teaspoons and 2 US tablespoons. One fluid ounce is related to the other US units of volume as follows:

1 US fl oz = 1/8 or 0.125 US cups

1 US fl oz = 1/16 or 0.0625 US pints

1 US fl oz = 1/32 or 0.03125 US quarts

1 US fl oz = 1/128 or 0.0078125 US gallons

Cups

A US cup is equal to eight US fluid ounces. It is also equal to 8.45 imp fl oz. It is used in the measurements of cooking units, nutrition labeling, and serving sizes in the US. The US cup is related to the other US units of volume as:

1 US cup = 48 US teaspoons

1 US cup = 16 US tablespoons

1 US cup = 1/2 or 0.5  US pints

1 US cup = 1/4 or 0.25 US quarts

1 US cup = 1/16 or 0.0625 US gallons

Also:

1 US cup = 236.588 mL

Pints

One US fluid pint is equal to sixteen US liquid ounces. Also,

1 US pint = 568.261 mL

One US pint is related to the other units of liquid volume as:

1 US pint = 2 US cups

1 US pint = 1/2 or 0.5 US quarts

1 US pint = 1/8 or 0.125 US gallons

Quarts

One quart refers to the quarter or one-fourth of a gallon. One quart is equal to 946.353 mL. A quart can be converted to any other US unit by using the following unit conversion:

1 US quart = 32 US fl oz

1 US quart = 4 US cups

1 US quart = 2 US pints

1 US quart = 1/4 or 0.25 US gallons

Gallons

One gallon is equal to 3785.41 mL. It is the largest US unit of volume. For example, a water truck can carry approximately 9000 gallons of water.

Figure 2 shows a summary of conversions of all the US standard units of liquids.

Figure 2 – Conversions for US Standard Units for Liquids

Mass

Mass is the amount of matter composed within an object. Mass is often confused with weight. Weight is the mass of the object due to gravitational pull. The following US units are used for the mass of an object.

Ounces

Ounces are different from fluid ounces. It is the smallest US unit of mass and is abbreviated as “oz.” It is related to the other US units of mass as follows:

1 oz = 1/16 or 0.0625 lb

1 oz = 1/32,000 tons

Pounds

A pound is also known as the “pound-mass” and is abbreviated as “lb.” One pound is equal to sixteen ounces. Also,

1 US lb = 1/2000 US tons

Pounds are the main unit to measure the weight of a person, animal, or object.

Tons

A ton, abbreviated as “t,” is the largest unit of mass. One ton is equal to 2000 pounds. Also,

1 US ton = 32,000 oz

For example, a truck has a mass of 3 tons.

Figure 3 shows the US unit conversions of mass and the US units in the SI unit of mass, i.e., kilogram.

Figure 3 – Conversions for US Standard Units for Mass and in its SI Unit (Kilogram)

Length

The measure of distance is known as length. It serves as a base unit in many systems of measurements from which many other units are derived. The metric unit of length in meters. The following US units are used to measure the length.

Inches

An inch is the smallest unit of length, abbreviated as “in.” It is related to the other US units of length as follows:

1 inch = 1/12 feet

1 inch = 1/36 yards

1 inch = 1/63,360 miles

For example, the length of a piece of paper can be measured in inches.

Also,

1 m = 39.3701 inches

Feet

One foot, abbreviated as “ft,” is equal to 12 inches. Also,

1 ft = 1/3 yards

1 ft = 1/5280 miles

For example, a car is about 14.7 feet long. Also,

1 m = 3.28084 ft

Yards

A yard is equal to 3 feet. For example, the length of a bed is about 2 yards. Also,

1 yard = 36 inches

1 yard = 1/1760 miles

One yard is equal to 0.9144 m.

Miles

One mile is equivalent to 1760 yards. This large unit of length is usually used to measure long distances between different places. For example, it takes 189 miles to travel from Rawalpindi to Lahore. Also,

1 mile = 63,360 inches

1 mile = 5280 ft

One mile equals 1609.34 meters.

Figure 4 shows all the US units of length converted from one unit to another.

Figure 4 – Conversions for US Standard Units for Length

Temperature

A temperature measures the extent of hotness and coldness in a quantifiable way. It is measured by a thermometer which has some thermometric substance and a reference point calibrated with a certain temperature scale.

The temperature can be measured in degrees of Celsius, Fahrenheit, and Kelvin. The US unit of temperature is Fahrenheit, and its SI unit is Kelvin.

Fahrenheit

To convert Celsius(°C) to Fahrenheit(°F) scale, multiply the temperature by 9/5 or 1.8, and add 32. For example, 35 °C is converted to Fahrenheit scale as follows:

35 °C = ( 35 ✕ 1.8 ) + 32 °F= 95 °F

To convert Kelvin(K) to degree Celsius, subtract 273.17 from the Kelvin temperature. For example, to convert 500 K into Celsius:

500 K = 500 – 273.15 °C = 226.85 °C

Examples

Example 1 – US Unit Conversion for Liquids

Convert 52 cups into quarts.

Solution

As:

1 cup = 0.25 quarts

52 cups = 52 × 0.25 quarts

52 cups = 13 quarts

Hence, 52 US cups are equal to 13 US quarts.

Example 2 – US Unit Conversion for Mass

Convert 8000 pounds into tons.

Solution

As:

1 lb = 1/2000 tons

8000 lb = 8000 × 1/2000

8000 lb = 4 tons

Hence, 8000 pounds are equal to 4 tons.

Example 3 – US Unit Conversion for Length

Convert 5000 miles into yards.

Solution

As:

1 mile = 1760 yards

5000 miles = 5000 × 1760 yards

5000 miles = 8,800,000 yards

Therefore, 5000 miles equals 8,800,000 yards.

Example 4 – US Unit Conversion for Temperature

Convert 450 Kelvins into Fahrenheit.

Solution

First, 450 K is converted in the Celsius scale as:

450 K = 450 – 273.15 °C

450 K = 176.85 °C

Then, 176.85 °C is converted in degrees Fahrenheit as:

176.85 °C = (176.85 °C × 1.8) + 32 °F

176.85 °C = 318.33 + 32 °F = 350.33 °F

Therefore, 450 K is equal to 350.33 °F.

All the images are created using GeoGebra.

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