At Blushproof®, we try to keep our sizing the same as the large retail stores, such as Woolworths and H&M, so if you know your size there, then you know your blushproof size. For example, if you buy ages 11-12 for your daughter then it'll be 11-12 on our site; or if you buy L for yourself, then you'll buy L blushproofs. (We've found that Jockey sizes are smaller than Blushproofs so a Jockey L will be the same as a Blushproof M)
If you do get the sizing wrong, no worries, as we have a 30-day hassle free exchange / return policy.
Here's a size guide for easy reference but as mentioned, we find the best method of choosing sizes is to buy the same size you'd normally buy.