Archimedes principle.
i dun think there is any answers near the source found by
QX179R..
to further complicate the problem, there are also holes within
sponges apart from it irregular shape...which there is no precise
way to measure
hence, by applying Archimedes principle of water displacement is
the best solution...
TS said air inclusive... so take it as just a irregular
solid...
Best bet is still water displacement but water displacement will
not measure the air space in the sponge... so TS will have to do it
twice...
1) First leave the spounge on a flat surface and slowly pour
water into it to see how much water it can absorb... I presume TS
know the actual step so I will not go into details... that
will be the volume of water it can absorb = the volume of air
space...
2) Then later use water displacement method as suggest by
Fcukpap to find the volume of the spounge...
3) add both up... volume of air space + volume of spounge =
total volume of the solid...