Small tends to be the ones you make somewhat insightful conversation with. These are the friends you are delighted to see, share a little of what's going on in your life. Usually there is an area of commonality or interest that you both can relate to. Fortunately, these friends do not demand too much emotional energy so you happily welcome them and easily say goodbye to them.
Medium is where the emotional energy begins to come into play. These require a little more depth in conversation which is normally encouraging. You talk about several levels of life and you can end up laughing or crying about the experiences that are so similar. Unlike the size small, these friends aren't quite as easy to say goodbye to so your time together can become lengthy by choice. However, you can go a few weeks at a time without meeting up while you still feel a certain closeness.
Large is when we start getting into the laughing until you cry, crying until you're snotting and a level of transparency that alleviates the fear of vulnerability we all feel. These are the friends you call when something great happens, something horrible happens or you just need to talk. These are the friends that understand when you can't always be there but also hold you accountable when you truly need to be there. These are your lifelong friends that you can count on all along as life happens. They challenge you, they encourage you, they help you see the good in yourself while highlighting where you can be better. You may only have a handful of these friends but their worth is priceless. You never have to say goodbye to these friends and it's a good feeling to know they'll be with you in life's journey.
There are also those who don't truly have a size because they're seasonal friends. These friendships can bring great joy but also great pain when the season comes to an end. Learn from these friendships, remember what these friendships produced in your life but do let go of of these friendships when it's time.
Final thoughts: Cherish your friends, don't cling to them. Love your friends, don't judge them. Have faith in your friends, don't limit them. Hope with your friends, don't doubt for them. Just be the size you're supposed to be, see how each friendship fits and enjoy it!