It is important to learn your jewelry sizing to make it easier for you to navigate today's jewelry world! With more people switching to online shopping, it will be a lot easier to find jewelry you love quickly when you can narrow it by size! Here are a few tools to help you find your sizes (note that google searching can also provide you with photo guides that I do not have license to).
There are many necklace sizing guides online, but I find very few that show my body type! Here is an easy way to figure out what necklace sizes look good on you: You will need 1-2 shoelaces and something to hang on them. Using a ruler, measure out the shoelace to popular necklace lengths (i.e. 16", 18", 24", 36", 48", etc....), tying two together if needed. Then thread whatever your item is onto the necklace to represent a pendant. You could use something like a roll of tape or your keys. Wrap this length around your neck and have someone take photos of you that you can reference when purchasing necklaces.
Using a piece of string or a shoelace, wrap around your wrist and then mark where the ends overlap or meet. Measure this on a ruler, and then you have your wrist size. Keep in mind that you'll want to add additional size for cuffs or bracelets that you want to dangle.
For bangles, measure around the largest part of your hand with the fingers bent in. Add a few cm to get it on easily. The easiest way to visualize this is to do a 'bangle sizing' google search. My bangles are listed by their circumference in centimeters.
For earrings length, you can measure and cut a piece of string, hold it to the earring hole you want it to hang from, and look in the mirror.