For your watch size; It is printed on the back of your watch or you can look in settings. Apple Watches only come in two sizes; You either have the smaller size or larger one. 

How to adjust to wrist; Look at the back of the bracelet you'll see what side the clasp opens. Open the clasp and remove how ever many links you need to adjust perfectly to your wrist.Guaranteed to fit!

Compatible with all Apple Watch Series.