How much did Apollo 11 weigh?

Anyone asking how much Apollo 11 weighed is usually referring to the spacecraft, which consisted of two independent vehicles. The Columbia command and service module weighed 28,801 kilograms at launch; that included the cabin, the main engine, the tanks, the fuel cells and the supplies for the journey. The Eagle lunar module reached 15,103 kilograms, split between a descent stage with a landing engine and legs, and a smaller ascent stage with the cabin for two crew members. Every extra kilogram would have cost fuel, so the lunar module was built as light as possible, right at the edge of what was viable.

Of that launch mass, only a fraction returned to the Pacific. The descent stage was left on the Sea of Tranquility as a launch platform, the ascent stage was jettisoned after the crew transfer, and the service module was discarded just before re-entry. All that remained was the cone-shaped command capsule, with the three men, their equipment and the lunar rocks: the only part built to withstand the heat of re-entry.

All of this was mounted on a Saturn V, which weighed many times more at launch. Most of that mass was fuel, burned in the first few minutes; the stages fell one after another into the sea or disintegrated. That's why figures about Apollo 11's weight only make sense with a clear point of reference: the rocket at launch, the spacecraft at launch, or the capsule at splashdown are completely different figures. In spaceflight, moreover, what matters is mass rather than weight, since it is mass that determines how much fuel each engine burn requires.