Biological Systems Engineering


Date of this Version



GENERAL AGRICULTURE B-4, Public Policy Issued April 1980, 15,000


The metric system was developed by government and scientific groups in 1790 to replace a host of diverse measuring systems used throughout France. By the early 1900's it had been adopted by most European and Latin American nations. By 1970 over 90 percent of the world, including all major industrial nations except the United States, had either adopted the metric system or had undertaken programs to implement it.

Use of the decimal-based metric system was made legal in the United States by Congress in 1866. Although some scientists and educators readily adopted the metric system, little acceptance was made by commerce or by the general public. After more than 100 years of debate and indecision by Congress, implementation of the metric system in the United States has begun. On December 23, 1975, President Gerald Ford signed the Metric Conversion Act, which is Public Law 94-168. This Law declared a national policy of coordinating the increasing use of the metric system in the United States and established a 17-member U.S. Metric Board to assist in the voluntary conversion of the metric system.

The Metric System

The metric system relates the measurements of length, area, volume and mass into a decimalized system. Additions and other numerical operations are simplified. In the U.S. customary system, numerical computations frequently require complicated conversions in length, weight or volume such as inches to feet, ounces to pounds and fluid ounces to gallons. However, except for moving the decimal, no conversion from unit to unit is required with the metric system.

Metric units for any given physical quantity relate to one another in multiples of 10 as does our monetary system. Prefixes are used to designate the amount of multiplication. Commonly used prefixes include kilo (1000), centi (0.01) and milli (0.001). The following example illustrates how the metric units for length relate to each other much as do parts of our monetary system.

The basic metric units used in everyday measurement applications are length, area and volume. The relationships between the metric and U.S. customary system for these units are described and illustrated graphically in the following text.

Length - The common metric units of length are the millimeter, centimeter, meter and kilometer. Rainfall, bolt sizes and other small dimensions are commonly expressed as millimeters. The centimeter is used for body dimensions and clothing sizes. Building perimeters, truck lengths and other similar sized objects are measured in meters. Distances between cities and towns are expressed as kilometers.

Area - The common metric measurements for area are square centimeter, square meter and hectare (10,000 square meters). Areas of glass panes are measured in square centimeters. Building and floor areas are measured in square meters. Farm land is expressed in hectares.

Volume - The common metric units of volume are cubic centimeter and cubic meter. Small engine displacements and liquid medicines are expressed as cubic centimeters. Larger volumes used in earth moving, ventilation and commerce are measured in cubic meters.