In short, Russia and China both have one in service aircraft carrier, both originally built by the Soviet Union. The former carries ~20 fixed wing aircraft and ~15 helicopters, the latter ~24 and ~12.

By comparison, the US have ten in service Nimitz class carriers, each 60% larger than its competitors and carrying on average sixty aircraft per ship, with their nine smaller Wasp class carriers functioning as helicopter/VTOL pads, housing approx two dozen of these per hull.