Another consideration in determining the length is to look at where the hair will be placed. Starting from the nape and up to where your first attachment/row will be placed, will determine your longest length. Going higher up to where your final attachment will be placed, indicates your shortest length.
Measure from the attachment point highest up going down to where you want the hair to end, and determine what needs to be trimmed or cut off. This measurement will indicate what length you would need if you wanted an even hair length without any layers.
