There are two main measurements that you will want to take when installing a transfer bench. The first is the length. You need to make sure that the bench is long enough to fit into your tub on the one side and stick out far enough on the outside of the tub to easily sit on it. The other measurement is the height, which can typically be adjusted. The transfer bench needs to not only be tall enough to fit over the side of your bathtub, but also so that it is comfortable and easy for you to sit down and stand up from it.