Is there a general capacity I can use for freight cars based on the length and height?
Number of gallons for tank cars based on length?
Other type of cars hoppers and covered hoppers?
Just general numbers will be fine.
Usually the cars are stenciled with the cubic foot capacity. Also stenciled are the height and width, and a few other things (varies by car type).
Tank cars are stenciled with their measured capacity.
After a while of looking and studying, identifying the specific variety of car becomes easy.