The heights and weights of things in the rule books always amuse me. The Disks of Mishakal from Dragonlance are described as being 160 disks of pure platinum, 18 inches in diameter and 1/16th of an inch thick each. That much platinum weighs 1,970 lbs. The War of the Lance book says they are surprisingly light at 15 lbs. If they were made of water, they'd weigh 92 lbs. So these plates are 1/6th as dense as water. Speaking of drowning, these are an excellent flotation device!
Fun fact: people are roughly as dense as water (high fat people a bit less dense, high muscle people a bit more dense, but most of us are just slightly less dense than water), so that's a quick and dirty method of determining how many cubit feet of volume someone takes up: divide their weight by 62.5 lbs/ft3.