The English System of Measurement

The English system of measurement grew out of the creative way that people measured for themselves.  Familiar objects and parts of the body were used as measuring devices.  For example, people measured shorter distances on the ground with their feet.
foot2

They measured longer distances by their paces (a "mile" was a thousand paces).  They measured capacities with common household items such as cups, pails, and baskets.  The word gallon comes from an old name for a pail.  

Unfortunately, these creative measuring devices allowed for different measurements to be obtained when different people measured the same items.  Eventually, a standard was set so that all measurements represented the same amount for everyone.

Length:
1 foot (ft) = 12 inches (in)
1 yard (yd) = 3 feet
1 mile (mi) = 5280 feet
1 mile = 1760 yards
Weight:
1 pound (lb) = 16 ounces (oz)
1 ton = 2000 pounds
Capacity:
1 tablespoon (tbsp) = 3 teaspoons (tsp)
1 cup (c) = 16 tablespoons
1 cup = 8 fluid ounces (oz)
1 pint (pt) = 2 cups
1 quart (qt) = 2 pints
1 gallon (gal) = 4 quarts

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Conversion Ratio (or Unit Factor): A conversion ratio (or unit factor) is a ratio equal to one. This ratio carries the names of the units to be used in the conversion. It can be used for conversions within the English and Metric Systems, as well as for conversions between systems. The conversion ratio is based upon the concept of equivalent values. In the example below, one foot is substituted for its equivalent measure of 12 inches.
foothold

Proportions are used when working with conversions.

Engconvertratio

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expin1 Convert 84 inches to feet.
A proportion can be set up using the appropriate conversion ratio. In a proportion the product of the means equals the product of the extremes. Use this "cross multiply" concept to find the answer.
engconratio
ANSWER: 7 feet


expin2 Find the number of cups in two gallons.
There is no stated conversion for cups to gallons, so we have to be a bit more creative. Since there are 4 cups in 1 quart, and 4 quarts in 1 gallon, we can set up the conversion ratio based on "quarts". Two gallons is 8 quarts.
cups in gallon
ANSWER: 32 cups

 

expin3 Convert 16 tons to pounds.
Set up the conversion ratio and solve for the missing value.
conversionratio83
ANSWER: 32,000 pounds

NOTE: As with all mathematical problems, there are other ways to arrive at these answers. Most other methods utilize the concept of the conversion ratio, but may be written in a different manner or calculated mentally.

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