Internal Volume of part

I'm trying to find out how many tiny cups I can fit inside of this part. I know each cup is .372 cu/in. If I try to do mass properties, this will not give me the internal volume of the part. I can make the part into a solid and check the volume then cut out the inside and re-check the volume of the second solid cut part, then find the difference, but I'm hoping SW can do this much easier.

SolidworksParts And Features