Here's as close as an example as I can give... Let's say at 3 weeks (20 days) flower your main cola is 4 inches long.... By the end of 8 or 9 weeks that same cola will be 12 inches or more.... It all depends on the strain ....
Triple in size unlikely but double very possibly now this is plant growth. As far as size of buds well you have bought an ounce of some chronic before so there you go those buds are buds just like what your mj plant will grow. Best example I can give