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.
Sometimes you need to convert from one unit of measure to another similar unit. How many inches are in 3 feet? How many ounces in 5 pounds?
Example 1: How many yards are in 15 feet?
There are 3 feet in
one yard, so the conversion ratio is 1
yd / 3 ft:
Example 2: How many cups in one gallon?
There is no direct
connection from cups to gallons. There are, however, 4 cups in one
quart and 4 quarts in one gallon. So the conversion
ratio could be:
Solving algebraically gives an answer of 16 cups.