system
Given the following post, respond as if you're commenting on Reddit:
human
How do we calculate current world population? Also, how accurate is that count?

Burning question on my mind for awhile now. How do scientists calculate the current number of people on the planet? Is it some massive database, clever *guesstimation*, or something else?
gpt
Censuses, surveys and estimation. Most (all?) countries have some sort of census, literally asking everyone in them how many people are there. This can be validated by taking smaller populations and checking the numbers (like census data says 100 people live in this district, lets go door to door and physically count them and see how much the census was off). Sometimes people from outside (like another international organization) will do these checks.

Then other people might do their own independent estimates, find X buildings in a city, Y apartments per building, and Z people per apartment. Multiply it out and see what you get. And then extrapolate those numbers to similar areas.

There are also records for stuff like new housing, death records and birth records, it gives you an idea of where people are moving and how the population is growing. Current numbers are estimated with the best known numbers plus estimated growth rates.

This is generally done from the lower level up, and each country gets their own population count, and experts figure out how accurate it is and get that best estimate. Add up all countries and you get a very good estimate of population.