If every person’s sole job was performing calculations (ie: working as the original definition of the word “computer”) and was able to complete one calculation per second1, the entire Earth’s population2 would be equivelant to ~2.5 laptop computers3.
1. One calculation per second assumes no time for transmission is required and that perfect synchronizing could be achieved
2. Population based on Google data of 6, 973,738,433 people
3. Based on my laptop, which has a 2.8 GHz processor