What percentage of the world's population watched the moon landing?

The mid-year population estimate for 1969 shows there were approximately 3,631,478,167 people on the planet. It is estimated that around 600 million people watched the Apollo 11 landing live on T.V. 600,000,000 / 3,631,478,167 = 0.16522.

Roughly 16.5% of the world population watched the first lunar landing.