Hand (length)

The hand is a non-SI unit of measurement of length standardized to 4 inches (101.6 mm). It is used to measure the height of horses in some English-speaking countries, including Australia,Canada, the Republic of Ireland, the United Kingdom and the United States. It was originally based on the breadth of a human hand. The adoption of the international inch in 1959 allowed for a standardized imperial form and a metric conversion. It may be abbreviated to "h" or "hh". Although measurements between whole hands are usually expressed in what appears to be decimal format, the subdivision of the hand is not decimal but is in base 4, so subdivisions after the radix point are in quarters of a hand, which are inches. Thus, 62 inches is fifteen and a half hands, or 15.2 hh (normally said as "fifteen-two", or occasionally in full as "fifteen hands two inches").

"Hands" may be abbreviated to "h", or "hh". The "hh" form is sometimes interpreted as standing for "hands high." When spoken aloud, hands are stated by numbers, 15.0 is "fifteen hands", 15.2 is alternately "fifteen-two" or "fifteen hands, two inches," and so on.

To convert inches to hands, the number in inches is divided by four, then the remainder is added after the radix point. Thus, a horse that measures 60 inches is 15 hands high (15 x 4 = 60) and a horse halfway between 15 and 16 hands is 15.2 hands, or 62 inches tall (15 x 4 + 2 = 62) Because the subdivision of a hand is a base 4 system, a horse 64 inches high is 16.0 hands high, not 15.4. A designation of "15.5 hands" is not halfway between 15 and 16 hands, but rather reads 15 hands and five inches, an impossibility in a base 4 radix numbering system, where a hand is four inches.

The hand, sometimes also called a handbreadth or handsbreadth, is an anthropic unit, originally based on the breadth of a male human hand, either with or without the thumb, or on the height of a clenched fist.

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