You can find the approximate internal dimensions of each Ring 3 size below. The above table should be used as a guide, and we don’t recommend using the dimension chart to pick an Oura Ring size.

So if you are the US size 5.5 or smaller in Nike, you may go half size up to get a comfy fit while switching to Nobull. And you can go with the same size for Nobull if you are the US size 6 or higher ...