I have a Rio Red Grapefruit which has about 100 buds. The early buds are about to open. The tree is about 4 feet tall. I would love to have all the fruit but would anticipate that alot of the buds will not produce fruit. How much fruit do you think a tree of this size can support. It currently has 3, one year old fruit left.

If you really want to know, count the buds and expect about 0.5 to 1 percent to produce fruit and keep them on the tree until maturity. - Millet

As usual, there are exceptions. When my grafted cara-cara first bloomed, there were only 8 flowers and then there were 8 good quality fruits, so the fruit set was 100%. Most of my new grafts are like that when they bloomed. The branch is large with few flowers, so that whatever few flowers there were would be 50% to 100% fruit sets. Now, as the they age and become larger like the rest of the canopy, they would have an overabundance of blooms and would set normal like the range described by Millet.