The most common unit for the height of a Ferris wheel would be meters or feet.

Here's why:

* Meters and feet are standard units for measuring height and distance. They are familiar and easily understood.

* Ferris wheels are typically quite large, so using smaller units like centimeters or inches would result in very large numbers.

While you could technically use other units like miles or kilometers, they are not practical for measuring the height of a Ferris wheel.