The Oura Ring 4 Sizing Kit allows for you to find the ideal size before purchasing an Oura Ring 4. It allows for you to try multiple sizes, wear for 24 hours, and find your most comfortable fit. Oura Ring 4 sizes are slightly different from standard ring sizes, so it is important to size. - Oura Ring 4 Sizing Kit is the ideal way to find the perfect Oura Ring size.- Oura Ring is available in sizes 6-13. There are no half sizes.- A properly fitting Oura Ring 4 will result in the highest data accuracy, comfort, and overall experience.