"jack" wrote in message
. ..
The barbeque sized ones; about how much are they full and empty?

There is TARE or just a T stamped on the collar (handle). That is the tare
weight, or the weight of the empty container. The contents are rated at
pounds, but sold as gallons, so add it up. Propane weighs approximately 4.2
pounds per gallon according to Wikipedia. Or take a bathroom scale, and
weigh the tank. Use a calculator and subtract tare weight. Or ask your kid
to do the math for you.

Steve