A pH scale measures pH in the range of:

A pH scale is a concept used to express the hydrogen ion concentration in a solution.

$\mathrm{pH} = -\log \left[{\mathrm{H}}^{+}\right]$

The pH ranges from 0 to 14. '0' represents a very acidic solution and '14' represents a very basic solution.

7 is the pH of a neutral solution.

Hence, the pH scale measures the pH in the range of 0-14.