Earth’s solid inner core begins roughly 5,150–5,200 kilometers below Earth’s surface, which is that same distance below the base of the crust, since the crust is only a few tens of kilometers thick in comparison.

Quick Scoop

  • The inner core starts at about 5,150 kilometers beneath Earth’s surface, at the boundary between the liquid outer core and the solid inner core.
  • Earth’s crust is only about 5–70 kilometers thick, so almost all of that ~5,150-kilometer depth is through the mantle and outer core, not the crust itself.
  • In total, the inner core extends from ~5,150 kilometers down to about 6,370 kilometers, the very center of the planet.

Mini perspective

In everyday terms, if you could drop straight down from the bottom of the crust, you would still need to travel over 5,000 kilometers through deeper layers before you reached the inner core.

Scientists infer these depths mainly from how seismic waves travel through Earth’s interior, since direct drilling barely scratches the crust.

TL;DR: The inner core is not just “under the crust” but begins over 5,000 kilometers below it, near the very center of Earth.

Information gathered from public forums or data available on the internet and portrayed here.