Even though uranus is bigger than earth why does earth have more gravity than uranus

Even though Uranus is bigger earth has more mass because earth is made up of rock and Uranus is made up of gas and  rock is heavier than gas because rock is a solid  has no room to for the molecules to move around while uraanus is made of gas which is lighter so the molecules can move around more freely which means that earth will have more mass and there for will have more gravity.