When I first learned the metric system I thought this match-up was a great
thing, too. Then I learned it wasn't really true.
Pre-1963, the liter was defined as one kg of water (at max density or 4 degrees C), but that was actually 1000.028 cc.
In 1963 the French committee in charge of the metric system voted, not to fix
this discrepancy by adjusting either the meter or the kilogram, but to sweep
it under the rug by redefining the liter as 1000 cc (and no longer related to
1 kg of water).
In my opinion, this continuing discrepancy means that the metric system is no
more "elegant" or "integrated" than the imperial system. Indeed less so, if
an imperial gallon weighs 10 pounds.
Now that they are thinking of getting rid of the standard kilogram block of
platinum/iridium, I urge the authorities to correct their original mistake
by reducing the size of the kilogram so that 1000 cc = 1 kg of water, thus
defining the kilogram in terms of the meter and integrating the whole
system of measurements better.
John David Galt
The comparison of the international prototype kilogram with secondary standards has an uncertainty limited to about 1 part in 10 to the tenth. A comparison with water can not be made with anything like that precision. For most practical purposes a cubic decimetre of water has a mass of 1 kilogram. The imperial gallon suffers from the same difficulty of definition in terms of a mass of water. It is in fact defined by a prototype container. (The definition of the imperial gallon involves the only factor of 10 in the entire imperial "system".)
