Understanding how much moisture to put into a pile soon becomes an
intuitive certainty. Beginners can gauge moisture content by
squeezing a handful of material very hard. It should feel very damp
but only a few drops of moisture should be extractable. Industrial
composters, who can afford scientific guidance to optimize their
activities, try to establish and maintain a laboratory-measured
moisture content of 50 to 60 percent by weight. When building a
pile, keep in mind that certain materials like fresh grass clippings
and vegetable trimmings already contain close to 90 percent moisture
while dry components such as sawdust and straw may contain only 10
percent and resist absorbing water at that. But, by thoroughly
mixing wet and dry materials the overall moisture content will
quickly equalize.

_Size of the pile._ It is much harder to keep a small object hot
than a large one. That's because the ratio of surface area to volume
goes down as volume goes up. No matter how well other factors
encourage thermophiles, it is still difficult to make a pile heat up
that is less than three feet high and three feet in diameter. And a
tiny pile like that one tends to heat only for a short time and then
cool off rapidly. Larger piles tend to heat much faster and remain
hot long enough to allow significant decomposition to occur. Most
composters consider a four foot cube to be a minimum practical size.
Industrial or municipal composters build windrows up to ten feet at
the base, seven feet high, and as long as they want.

However, even if you have unlimited material there is still a limit
to the heap's size and that limiting factor is air supply. The
bigger the compost pile the harder it becomes to get oxygen into the
center. Industrial composters may have power equipment that