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. 

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

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.

Proportions are used
when working with conversions.

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. 
ANSWER: 7 feet 


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. 
ANSWER: 32 cups



Convert 16 tons to pounds.
Set up the conversion ratio and solve for the missing value. 
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. 