Useful Tools
Global Interference will show any overlapping volumes in an assembly
Analysis tab > Global Interference
Mass Properties will give you the volume/weight of a component or assembly. If your after the weight you will need to set a material to the model through File > Prepare > Model Properties. If your just after the volume just leave the defaults.
Analysis tab > Mass Properties
The figure for volume is likely to be shown as an exponential figure in the modelling units.
Example: VOLUME 8.5010447e+03 MM^3 , move the decimal place plus 3 places to give 8501.0447 MM^3. Remember to convert this figure if you need different units:
1000mm^3 = 1cm^3 therefore 8501.0447mm^3 = 8.5cm^3 to 1 dp