Introduction and Overview
Density describes the mass per unit volume of a substance. The formula for density is mass/volume. Thus, density can be represented by any mass unit divided by any volume unit, but only the common ones have any practical application. The units in this converter are based on the most common mass and volume units of today. For a description of the various units, see the megaConverters #1 Mass & Weight and #3 Volume.
The original definition of a kilogram was the mass of one exact liter of water at maximum density. That is no longer the case. The kilogram was fixed at a specific mass and the meter at a specific length. A liter is now defined as a cubic decimeter. The exact density of water is almost, but not quite, 1 kilogram per liter.
Occasionally, people in olden days defined certain weights by how a certain volume of a particular substance weighed. The gallon-weight was based on a gallon of water, and the barrel-weight was based on a barrel of flour. These uses counted on the density of the substance to remain the same. For more information, see the various megaConverters on ancient and foreign measures.
For a more comprehensive treatment of measurements, find "NTCs Encyclopedia of International Weights & Measures" by William D. Johnstone at your local library. For a better discussion of density, see any college physics textbook.
* 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! For a more complete listing of ancient, foreign, and obsolete measures, download our 'megaSpreadsheet' of conversions in MS Excel format.
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.