We don't know the exact number of planets in the Milky Way, but it's estimated to be in the trillions.

Here's why:

* Exoplanet discoveries: Astronomers have discovered thousands of exoplanets (planets outside our solar system) using various methods like the transit method and radial velocity method.

* Statistical estimations: Based on the rate of exoplanet discoveries and the estimated number of stars in the Milky Way (around 100-400 billion), scientists have extrapolated that there could be multiple planets per star on average.

However, these are just estimates. The Milky Way is vast, and we've only explored a tiny fraction of it. It's likely that the actual number of planets is even higher than current estimates.