2-10 Inchesis the length I like to use for adding some length and thickness to the front part of the sides of the head to make "The Bob Haircut" appear to be more of an angle. Generally a 20-pk. if I-Tips is sufficient for this type of service. General cost can be as low as $85!!!
18 Inchesis the average length for hair extensions. It falls a little below the bra strap, and can be cut to blend in with shoulder length hair, this would be the length I recommend.
20 Inches will fall at the waist area. This length can be used for people with hair anywhere below shoulder length. If your hair is shoulder length or above, 20 inches wouldn't be a good fit because of the excessive cutting that would need to be done. Also, it could very well look unnatural after the blending process. If your hair is past your shoulders, you may like to try 20 inches for extra length.
22 Inches is for people who already have generally long hair but want it longer. It will fall just above your belly button area. If your hair hits your bra strap or below, you qualify for 22 inch hair.
24 Inches This is very long and meant for people with long hair who just can't get it long enough. 24 inches will fall just above your belt loops.