The thickness of the asthenosphere varies depending on location and depth. It's not a clearly defined layer with a fixed thickness.

Here's a general idea:

* Average thickness: Around 60 to 200 kilometers (37 to 124 miles)

* Depth range: Typically begins around 100 to 150 kilometers (62 to 93 miles) below the surface.

* Variable thickness: Can be thinner under mid-ocean ridges and thicker under continents.

It's important to note that the asthenosphere is not a solid layer. It's a zone within the upper mantle that behaves like a very viscous fluid, allowing the lithospheric plates to move.