Angstrom mil hand
link span cubit
vara fathom rod, perch, or pole
surveyor’s chain furlong cable length
std nautical mile league nautical league
US Survy Foot    

Length megaConverter #2

Introduction and Overview
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Units of common measurement vary widely, from time to time, and place to place. Most units of measurement started as a reference to a physical object or concept. The foot was the length of a man's foot, the inch was the width of a man's thumb, a furlong was the length of a plowed furrow in a field, an acre was the amount of land a man and two oxen could plow in a day, etc. At first, most measurements were only approximations, but eventually many country's governments set each at a specific standard to make commerce possible and fair. Often, when people settled new lands, they used the names of old measurements, but set their own standards. Other times, similar sounding measurement names in different countries had greatly different values. Some measurements were derived from other types of measurements, such as a barrel weight being the weight of a barrel of flour. Often, the same measurement had different values depending on the material being measured, such as a wine tun and a beer tun, or a hank of wool and a hank of cotton. These differences made sense to the people that used them, but they seem odd today.

A Frenchman first defined what he called the 'meter' as one ten millionth of the distance from the North Pole to the equator along the Prime Meridian. It was later defined, in a more precise method, as so many wavelengths of a certain color of light. A liter was originally defined as a cubic decimeter, and a kilogram was defined as a liter of pure water at a specified temperature. Later, the standard was changed such that a kilogram mass became the standard and the liter was derived as the volume of a kilogram of water. This has caused the liter to become slightly more than a cubic decimeter.

The International System (SI) was first proposed in France in the 17th century, but was not adopted by France until 1795. The system defined that there was only one standard in each measurement type and each unit greater or less was a power of ten. This made conversions between units much simpler. During the 19th century, several countries made this system their standard, but notably not Britain or the US. In 1965 Britain began changing to the metric system as a condition of membership in the European Common Market. The US government, recognizing the problems of international trade, officially made the metric system its standard in 1975.

Still today, units of common measurements (non-metric) are used throughout the world. It would be hard to forget the foot, yard, mile, quart, gallon, or acre because so many physical objects were based on them. And for convenience sake, it will always be easier to say "a cup" than "two deciliters." It is easier to envision a mile than a kilometer because fence rows, city blocks, and farmland measurements were originally based on the mile.

* Much of our written history still refers to things in common units. The Bible does not refer to meters or kilograms, but to cubits and stadia, or shekels and drachma. Wouldn't it be nice to know what they were talking about way back then? Now you can use megaConverter! This megaConverter is specifically for mass and weight measurements commonly used today in the US, Britain, and by the SI system. See megaConverters Ancient Length #26 and Foreign Length #27 for length conversions common in ancient times and foreign countries. For a more complete listing of ancient, foreign, and obsolete measures, download our 'megaSpreadsheet' of conversions in MS Excel format.

For the most comprehensive treatment of measurements, find "NTC's Encyclopedia of International Weights & Measures" by William D. Johnstone at your local library.

Glossary of Conversions:

The Angstrom is commonly used in physics to express the size of atoms.

A mil is 1/1000 of an inch. It is used in machine tolerances. Numerous countries have a unit called mil, but it's more related to the mile or league.

The hand is typically used to measure the height of a horse from hoof to shoulder.

A link is used by surveyors and is 1/100 of a surveyor's chain. Also known as a Gunter's link.

A span is often used in cloth measure and is the width of a spread hand.

A cubit is an ancient measurement approximately from the elbow to the tip of the middle finger.

A vara is common in Latin America and came from Spain. Its value varies from country to country.

A fathom is a marine unit of water depth.

rod, perch, or pole
A rod, perch, or pole is a surveyor's unit. One acre is a rod wide by half mile long.

surveyor's chain
A surveyor's chain is four rods or 100 links. It was usually an actual chain of 100 iron links.

A furlong was the length of a plowed furrow. It is commonly used in horse-racing.

cable length
A cable length is a marine measure and represented the length of the cable on most sailing ships. Still used at sea, the length varies by country.

nautical mile
A standard nautical mile is a marine measure and represents 1/60 of a geographic degree. The International Nautical Mile is more correct but the standard nautical mile is commonly used.

A league is an ancient unit that varied from 2.5 to 4.5 miles. It referred to marching distances usually.

nautical league
A nautical league is 3 standard nautical miles.

US Survey Foot
The difference between the Standard Foot and the US Survey Foot is two parts in a million, i.e.. 1 standard foot = 0.999998 US Survey Foot. This may not sound like much but in the surveying profession this can mean great differences. The main gist of the difference is noticed when converting units with SI system units. The proper calculation is this:

1 meter = 3.28083333333333333333333 US Survey Feet
1 meter = 3.2808 Standard Feet (exactly)
1 US Survey Foot = 0.30480060960 Meter
1 Standard foot = 0.3048 Meter (exactly)

another way of looking at this difference.

( 39.37 (exactly) / 12 ) x distance in meters = distance in US Survey feet
( 12 / 39.37 (exactly) ) x distance in US Survey Feet = distance in meters

The US Survey Foot is the original length of the foot used in the US. The definition of the meter was changed in 1960, thus the foot was changed as well. The US Survey foot was kept to insure proper relationships with recorded measurements.

Note: Because of round-off errors, converting from very large units to very small units or vice-versa may not be accurate (or practical). Conversion factors can be found by converting a quantity of 1 unit to another unit several steps above or below the first. You may need to string several conversion factors together to find the factor from a very large unit to a very small unit, and then you can use a calculator with sufficient digits to find your answer.