How to get a list of all the possible thumbnail sizes set within a theme

What function can I use in a plugin to get the dimensions of every image size (in an array preferably) that is defined in a child theme?

Just for clarification I am not asking how to create a new image size.

Found it here. The answer is:

global $_wp_additional_image_sizes; 
print '<pre>'; 
print_r( $_wp_additional_image_sizes ); 
print '</pre>';