okay so we now how to find density and mass,

but how would you find the volume of a pumkin?
Depends... You must first know the length, length base and height, the formula is;
V=blh
Or you can treat it as close as you can to a sphere. You could make it relly accurate and go into integral calculations using the inegration of
∫ f(x) d(x)
But that would be tedious so i would stick to a sphere, and ignore the errors;
V = 4πr3/3
Is how you calculate it.