I like to fold my border fabrics in different widths and "audition" them to see what looks best to me. Taking pics help. I upload them to the computer and view them side by side. I find it's easier for me to decide that way. I often use an inner border, usually 1-1/2" or 2" finished, depending on the top. Most of my borders vary between 4"-6" unless I am doing a scalloped border. Those I cut wider usually.