A hair graft produces 1,2 or 3 hairs.
"Follicular units" is the term given to the natural groupings of hairs in the scalp - and these follicular units contain 1-3 hairs. They generate 1-3 hairs
How many hairs grow in each graft
Of course the answer to that question should bee as many hairs that the graft contain, 1,2 3 or 4 hairs. If everything is done correctly, we expect 100% of the transplanted hair to grow but from a practical point of view, I generally expect over 90%, may be 99%. We never really can count the number accurately unless we did less than 10, then we would know for sure
Number of grafts vs number of hair
There are two different ways to estimate the amount of hair needed. The golden standard by most doctors is per number of grafts or number of follicular units. The second way that some doctors use is the number of hairs transplanted, In each graft, there may be one, two or three hairs, and depending on the number of hair in each graft, they are used appropriately in the recipient area. However, it is also good to know how many hairs were transplaned. This way you can have an idea of the overall look after the hair grows in, keep in mind that 2000 grafts at one clinic may give a very different result at another clinic depending on what proportion of one, two, or three hair grafts was used. For example if 2000 grafts were all one hair units the total number of hairs would yield 2000 hairs. But let say with 2000 grafts, there was 500 ones, 500 twos and 1000 three hair units, in this case the total hair would be 4500 hairs. So it is important to know both the number of grafts and also the total number of hairs that was transplanted.
If you have one single graft implanted and it has one single hair in the graft, then one single hair should grow.
If the graft was damaged during surgery, NO hair will grow.