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Chain (unit)

math Maturity 11-13 Next article →

A chain is a special way to measure distance. It is a unit of length used in the United States and the United Kingdom. One chain is 66 feet long, which is the same as 22 yards. You can think of it as being broken into 100 smaller pieces called links. If you want to measure very long paths, you can use chains to find the total length. For example, ten chains make up one furlong. There are also 80 chains in one statute mile.

Bridge miles and chains
Bridge miles and chains

Measuring land can be a very hard job without the right tools. Long ago, people used a tool called a surveyor's chain to make sure measurements were correct. This tool helped them map out straight lines and curved paths. The distance measured along these lines is sometimes called chainage. It is a bit like how an odometer in a car tells you how far you have traveled. By using these chains, people could mark exactly where one piece of land ended and another began.

This method of measuring was made famous by a man named Edmund Gunter. He was a polymath, which means he was an expert in many different subjects. In 1620, he developed a way to survey land using a 66-foot chain with 100 links. This specific tool became known as Gunter's chain. Before this, different places had different lengths for their miles. For instance, a Scots chain was about 74 feet and an Irish chain was 84 feet. These different sizes were replaced by the standard system in 1824.

History shows that these chains traveled all over the world. British settlers took the idea to many new countries. In the United States, a law called the Land Ordinance of 1785 made the chain a required tool for surveying. This helped leaders like Thomas Jefferson plan how to divide up large areas of land. Even today, you can find traces of this history in many places. In Australia and New Zealand, many old roads and building lots were measured using chains.

Bridge miles and chains
Bridge miles and chains

We still see the chain used in interesting ways today. In the United Kingdom, railway workers use miles and chains to show where bridges or stations are located. A bridge might be at a spot marked as 112 miles and 63 chains from the start of the track. In North America, farmers sometimes use measuring wheels that are based on the chain. Even wildland firefighters use the chain to measure how fast a fire spreads. In the sport of cricket, the distance between the stumps is exactly one chain long.

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