BJJ GI Size Guide – How to choose the correct Size BJJ GI. Probably the most common questions we get asked are to do with GI sizing. The GI size chart can sometimes be a little confusing with both height and weight mentioned and with some people falling between various sizes and others being too tall and slim or too short and big to fit somewhere in the chart. These are just some of the problems people face when trying to pick the right size. Below we will show you how to choose the right size no matter what your build is.