Answer :

Work out the area of it as if it were 2 dimensional them multiply by the depth.
You can pour water into it. Then check how much the water needed to fill it weights. [tex]1 dm^{3} [/tex] weights 1 kg.

So if water weight 300 grams, it means that the volume is [tex]0,3 dm^{3}=300 cm^{3}[/tex]