echo custom fields into array

Hi I have the custom post type ratings, which has been set to allow users to leave feedback, with this is the option of a 1-5 star rating.

I’m trying to echo all the custom field values of “rating_star” into an array in order to get the average based on post count, is there are simple way of getting the total based on all submitted rating values? or am I going about this the wrong way?

Cheers