Science and commerce use four basic kinds of measurement: nominal, ordinal, ratio and interval. Nominal describes different qualities: lion, tiger, bear. Ordinal describes qualitative degrees: agree, no opinion, disagree. Ratio describes mathematical comparisons: China has five times as many people as the United States. Systems of weights and measures are examples of interval measurements that proceed along scales in which the distance between numbers is equal: There is one inch between one and two inches; and there is one inch between 11 and 12 inches.
Even though the metric system deals with factors of 10 (100 centimeters in a meter, 1,000 milliliters in a liter), and the U.S. Standard system deals with factors of three, four and 12 (3 feet in a yard, 4 quarts in a gallon, 12 inches in a foot), they both measure the same things. In two dimensions, both systems measure length and area. Length and area are spatial measurements. Length is the distance between two points; and area is the total surface within a set of containing lines. A line might be measured in centimeters or inches, and an area might be measured as a square yard or a square meter; but the measurement is still of lines and areas.
Both systems measure spatially in three dimensions. That means both systems have interval measurements for volume and capacity. While volume and capacity are related, in each system they are differentiated similarly. For example, in the metric system, liters are a capacity measurement, while volume is still expressed as cubic forms of two-dimensional measurements – a cubic meter. Likewise, in the U.S. standard system, capacity can be expressed as pints or quarts, while volume is expressed in cubic feet or cubic yards.
The metric and U.S. standard systems both measure weight. Weight is a determinate mass of an object times its size, measured by how much gravitational pressure it exerts on a scale. While each system has distinct graduations for naming weights, and distinct ratios between these graduations (12 ounces in a pound, 1,000 grams in a kilogram), they both have an interval system of weight measurement. Both systems also use the word "ton" to describe very large weights, though the term describes different weights in each system.