The number of fingers that should fit under your watch depends on the size and shape of your wrist. Generally, you should be able to comfortably fit two fingers between the band and your wrist. If you can't, then it's likely too tight; if there is a lot of extra space, then it's probably too loose. It is important to find a watch that fits properly as an ill-fitting watch can cause discomfort or even injury over time. Make sure to try on different sizes and styles until you find one that fits perfectly.