What Is Metric to SAE?

As anyone who has ever worked on a car or even just bought a set of wrenches knows, tools come in two different standards of measurement: metric and SAE. Metric measurements are in millimeters, centimeters and meters, whereas SAE measurements are in fractions of an inch. Because two different standards of measurement are used, it is sometimes necessary to know how to convert metric measurements into SAE measurements or vice versa.

Ancient Systems of Measurement

People have been measuring things for as long as history records. Originally there was no standard way of measuring things. Different people in different areas of the world used whatever methods seemed easiest to them. This created many different systems of measurement, often using standards coming from different jobs, such as agriculture and sailing. The grain, an old-fashioned unit of weight, was the weight of an average grain of wheat or barleycorn. The league was a measure of how far the average person could walk in an hour. The foot, widely used by many primitive societies, was simply the length of someone's foot. The fathom, a measurement of depth, comes from sailors measuring rope by stretching lengths of it between their hands.

The Imperial System

As trade between different parts of the world increased, the differences in local standards of measurement became an increasing problem. In England, metal weights and measures were made to solve this problem with a set of measurement standards that everyone could agree to use. This was the basis of the Imperial system of measurement, which uses feet as the standard unit of length and pounds as the standard unit of weight. It became the official system of measurement in England and later, in modified form, in the United States.

SAE

In the early part of the 20th century, the manufacture of automobiles started to become widespread. Dozens of different automotive manufacturers existed all across the United States, each with their own sets of standards. The need to all adopt the same units of measurement was quickly seen, and when these engineers and manufacturers banded together to form the Society of Automobile Engineers, they adopted the imperial system of measurement as their standard. Since then the imperial system has also been called the "SAE system."

The Metric System

In the 17th century, France was in much the same position that England had been. A patchwork of inconsistent standards of measurement impeded business and allowed rampant fraud. Every region was loyal to its own system of measurements and would accept the use of no other system. In 1670, it was suggested to create a new system of measurement based on the size of the earth, free of individual regional ties. Following the French Revolution, the French adopted this measurement system as their standard. Because it was based on the decimal system it was easier to use than the imperial system and eventually became the standard system of measurement for most of the world.

Conversion

Because the majority of the world uses the metric system and the United States does not, mechanics and engineers in the United States often need to convert between different systems of measurement, as most imports are in the metric system. This can lead to a host of difficulties, from the minor inconvenience of having to buy two different sets of tools to major disasters such as the loss of the Mars Climate Orbiter in 1999, which was due to its computers using unconverted units, according to Robert Nelson of New Mexico State University.