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The Inch System

The Imperial Inch System.


The history of the current inch system dates back to the early 10th century when King Hywel the Good standardized the method of measurement in England by standardizing the inch to 3 barley grains aligned lengthwise. Later in 1066 the foot was standardized to 12 inches from the previous 13 inch foot, and the mile was standardized to 5280 feet in 1592.

Although this all seems complicated. Remember the English system of measurement was based on the old “relative” measurement method. A inch was based on barely as the average length over any random 3 grains will give a more or less equal inch. Since at that time things were made one at a time by the tradesman, it did not matter if the production of a single part was 1/8” off or 1/4” off the measurement as the parts were not meant to be interchangeable!

Another measurement still in use today that is based on the barley grain is the weight measurement of the “grain” which is equal to the weight of one barley grain. One pound in the English system is deemed to be 7,000 grains.

Richard I of England developed the first standardized size for the yard, based on 36 inches. He did his by distributing iron yard sticks that were made to all the same length and sent them throughout the country to make the yard standard across his kingdom. This standard remained the same till Elizabeth I of England created new yard sticks in 1588. She produced new standards and distributed them around the country. Although the master was damaged and repaired since, it is only off by 0.010” compared to today's yard. Which is less then 0.004” per foot. Making this measurement about as accurate as one can expect from the production methods available at the time to produce these standards.

Length Units:

  • 1 foot = 12 inches
  • 1 yard = 3 feet = 36 inches
  • 1 rod = 16 feet 6 inches
  • 1 chain = 4 rods = 22 yards = 66 feet
  • 1 furlong = 10 chains = 220 yards = 660 feet
  • 1 mile = 8 furlong = 1,760 yards = 5,280 feet
Area Units:
  • 1 acre = 43,560 square feet
  • 1 square mile = 1 section = 640 acres
Weight Units:
  • 1 pound = 16 ounces = 7,000 grains
  • 1 troy pound = 12 troy ounces = 5,760 grains
Volume Units:
  • 1 tablespoon = 3 teaspoons
  • 1 ounce = 2 tablespoons
  • 1 cup = 8 ounces
  • 1 pint = 2 cups
  • 1 quart = 2 pints
  • 1 gallon = 4 quarts
  • 1 oil barrel = 42 gallons (Not 55 gals, so remember this when you hear about the cost for a barrel of crude!)
Dry Volume:
  • 1 pint = 33.60 cubic inches
  • 1 pack = 2 gallon
  • 1 bushel = 4 packs
  • 1 barrel = 7056 cubic inches.

The Inch, on the international stage did its last change in 1959. During World War 2 the issue of having a slightly different American Inch and a different British (Imperial) Inch lead to a few difficulties. Since the British Inch was equivalent to 25.399956 millimeters, and the American Inch was approximately 25.4005 millimeters, the Canadian parliament adopted a Inch in 1951 approximately 2 parts in 10^6 different from the British and American inches. This standardized the Canadian Inch in 1951 to 25.4mm. In 1959 the International Inch was adopted as the 25.4mm which is what the Canadian Government adopted 8 years earlier.

The Inch has gone through a very long history. It has lasted through over a thousand years, and once one understands how the Inch is used, it is simply a matter of applying it. Over the course of this section of the website as I upload more content the Imperial system will be discussed in great detail. Do not panic if you do not understand what the Inch really is. Over the course of this section the Inch and the Meter will be used in various examples to stress the interwoven relationship between the 2 systems in the shop.