I placed the plants under different treatments and i would like to see the percentage of regeneration and weights of regeneration plants compared to the control plants
In that case, you compare weights of regenerated plants from control plates (medium has no treatment) and non-control plates (medium has treatment). You probably need to measure a certain number of plants from each group, then average the weights from them, then compare.
First, we need to clarify the terms you used. What did you mean by 'regenerate'? Did you mean regenerate plantlets from callus? If so, a callus can regenerate into many plantlets. There might be some weight variations among these regenerants. So, use a single plant for comparison doesn't make sense.
In your another question, I saw you mistook 'regenerate' with 'germinate'. That is way I am asking.
By the way, in science, when a parameter is compared between two groups, usually people use data collected from a number of samples (not from only a single plant). Then use statistics to analyze the data from those groups to see whether the difference between these two groups is statistically different.