How many planets are in the universe? How is this number estimated?

Firstly, given that the Universe is 13 billion years old and that no information can travel faster than the speed of light, all we currently know about is our neighborhood, which is 13 billion lightyears. This distance is known as the horizon, and all we can do is speculate as to whether there is finite or infinite space behind it. If the answer is infinite, then the most likely explanation is that there are infinite planets in the Universe, but we will never be able to know for sure.

How many planets are there within the horizon? This is what we are willing to learn about the cosmos and what we could know if we were intelligent enough.

Given that the region's volume (a sphere with a radius of 13 billion light-years) is known, the following information needs to be ascertained:

the average number of galaxies in a unit volume, or the galaxy density

the average amount of stars in each galaxy

the average planet to star ratio

The answer can be found by multiplying all of these, but since they are all still very tentative, we can only say for sure one thing at a time: there are an enormous number of planets that defy human comprehension.

The precise number of planets in the universe is unknown, but estimates range from billions to trillions of planets in the observable universe. These estimates are based on astronomical observations of planetary systems in our own galaxy and extrapolations from those observations to estimate the number of planets in other galaxies. Exoplanets orbiting stars in our galaxy are detected using a variety of techniques, including gravitational microlensing, direct imaging, and transit observations.