The best current answer is billions to tens of billions of potentially habitable, Earth-sized planets in the Milky Way, with one widely cited estimate around 8.8 billion for Earth-size planets in the habitable zone of Sun-like stars, and broader estimates rising to about 40 billion when cooler red-dwarf stars are included.

What that means

  • Earth-sized means roughly the same physical size as Earth.
  • Habitable usually means in the star’s “Goldilocks zone,” where liquid water could exist on the surface.
  • Different studies use different assumptions, so the number changes a lot depending on whether you count only Sun-like stars or also red dwarfs.

Practical takeaway

A safe plain-English answer is: probably at least several billion, and maybe around 10–40 billion such planets in our galaxy. That is an estimate, not a count of confirmed planets, because astronomers still have to infer most of them statistically rather than directly observe them.

Why estimates vary

  • Some research counts only planets around stars similar to the Sun.
  • Other research includes smaller, cooler stars, which are much more common.
  • “Habitable” is also a fuzzy term, because a planet can sit in the right zone and still be too dry, too windy, or have the wrong atmosphere for life.

TL;DR: The Milky Way likely has billions of habitable Earth-sized planets , and a commonly quoted range is about 8.8 billion to 40 billion depending on the method used.