Are the gas 'giant' planets actually the size of earth, but with humongous mother-f atmospheres?

I'm assuming by you're asking if the solid material of the gas giants are the size of earth and the rest of their mass are made up of gases. Well, conventional knowledge tells us that these gas giants may in fact be made up completely of gases and have no actual solid material. So they're basically just one big atmosphere with molten cores. The gases get thicker and denser as you get towards the center of the planets and since we're not 100% of the make-up of their cores, we still not sure whether or not we can actually even land on those planet.