I assume you are asking to understand how long the hair in the back should be before an FUT procedure. In this case about an inch is long enough to cover the sutured area. If you are trying to camouflage FUE, where a greater area tends to be shaven, then you have two options which you can discuss with your surgeon. Option one is to shave a large box area in the back of the head only to the height that your hair can cover. Option two is to shave linear areas about 1/2 inch high and allow the hair to "shingle" over each area. This approach requires more preparation and can sometimes slow down the extraction process leading to less yield, but it will allow you to have FUE with shorter hair. You can also consider long hair FUE but this can be much slower than standard FUE meaning more cost for less hair in general.