It's tricky to give an exact percentage for the Earth's surface covered by mountains because there's no universally agreed-upon definition of what constitutes a "mountain."

However, here's a general idea:

* Roughly 24% of the Earth's landmass is considered mountainous, based on elevation and terrain.

* This translates to about 10% of the Earth's total surface area, considering the oceans cover the majority of our planet.

Keep in mind:

* This percentage can vary depending on the definition of a mountain (e.g., minimum elevation, specific geological features).

* It excludes areas like plateaus and hills, which can be high but don't meet the criteria of a true mountain.

So, while a precise number is hard to pinpoint, it's safe to say that mountains cover a significant portion of the Earth's landmass, though a relatively small percentage of its total surface.