   SEARCH HOME Math Central Quandaries & Queries  Question from chris: how do you find how much a 4 foot diameter cylinder 4ft tall with a thickness of 6 inches weigh Chris,

Answer: Put it on a scale. :)

Seriously, we cannot answer your question without knowing what the cylinder is made from. The density of the material multiplied by the volume will give its weight.

The volume we can calculate:

Assuming the "thickness" is inwards (that is, the outside diameter is 4ft, but the inside diameter is 3 ft), we can subtract the volume of the empty inside from a full cylinder outside. The volume of a cylinder is the square of its radius times pi times the height. So the volume of your empty cylinder is (22)(pi)(4) - (1.52)(pi)(4). This is about 22 cubic feet.

If your cylinder was made of concrete, which is typically about 144 lbs per cubic foot, then it would weigh 22 x 144 = 3168 lbs. If it was made of styrofoam, then it would weigh 22 x 6.25 = 138 lbs, since the density of styrofoam is about 6.25 lbs per cubic foot.

Hope this helps,
Stephen La Rocque.     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.