# How I can measure an error in a bar plot?

This is my barplot. Model(red) is my estimated frequency at each X-axis vale (0-19) and actual is the frequency at each X-axis vale. How I can measure error of this estimating work in barplot?
If I use mean percentage error it does not consider the each size of bar. How should I solve that?? Of course, I have a data about expected frequencies and actual frequency at each value (X-axis).