That while the kilogram is defined in terms of three fundamental physical constants, the imperial equivalent, the pound is legally defined as exactly 0.45359237 kilograms

Pound (mass)

For the unit of weight or force, see Pound (force). For the monetary unit, see Pound (currency).

“lb.” and “lbs.” redirect here. For other uses, see LB and LBS.

The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces. The international standard symbol for the avoirdupois pound is lb; an alternative symbol is lbm (for most pound definitions), # (chiefly in the U.S.), and ℔ or ″̶ (specifically for the apothecaries’ pound).

The unit is descended from the Roman libra … Continue Reading (13 minute read)

9 thoughts on “That while the kilogram is defined in terms of three fundamental physical constants, the imperial equivalent, the pound is legally defined as exactly 0.45359237 kilograms”

  1. mandy009

    And the kilogram itself was until recently one of the most “loosely”-defined units. This month is the two-year anniversary of its update to fundamental forces.

  2. nathanatkins15t

    Similarly the inch is defined as 2.54cm
    I think most typical imperial units have been defined by SI units since the 1950’s

    Edit, from teh wiki: In 1930, the British Standards Institution adopted an inch of exactly 25.4 mm. The American Standards Association followed suit in 1933. By 1935, industry in 16 countries had adopted the “industrial inch” as it came to be known,[30][31] effectively endorsing Johansson’s pragmatic choice of conversion ratio.[27]

    In 1946, the Commonwealth Science Congress recommended a yard of exactly 0.9144 metres for adoption throughout the British Commonwealth. This was adopted by Canada in 1951;[32][33] the United States on 1 July 1959;[34][35][36] Australia in 1961,[37] effective 1 January 1964;[38] and the United Kingdom in 1963,[39] effective on 1 January 1964.[40] The new standards gave an inch of exactly 25.4 mm, 1.7 millionths of an inch longer than the old imperial inch and 2 millionths of an inch shorter than the old US inch.[41][42]

  3. mariuszmie

    So the pound is just a ‘fancy’ old-timey nick name for 0,4536 kg or for 454 grams

  4. csdx

    Being defined by physical constants is actually a fairly recent development for the kilogram. I believe it was the last SI unit to be (re)defined in terms of physical constants, previously it was defined by reference to an actual object, Le Grand K.

  5. Safebox

    And the kilogram was only defined with maths in 2018. Before that it was the last measurement to be defined by a physical unit, which was actually shifting constantly because of gathering and losing molecules despite being in a glass dome.

  6. kevinclements

    Wouldn’t this mean the pound is defined by three fundamental physical constants as well then?
    If A = B and B = C, then A = C

  7. Background-Half-2862

    This is because the metric system is superior system.

  8. Ulgeguug

    HAHAHA FOOLS! WE HAVE DEFINED THE KILOGRAM AS 2.20462 LBS! You can’t stop us we’re cRaZy

  9. CreedogV

    ITT: People misunderstanding defining the pound as “deriving the pound” instead of “standardizing the pound”.

    Metric went through all the trouble of making their system really gross so that it could be precise and standard strolled in and said, “Thanks for doing the hard work. Let me just add my name to your homework.”

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