Perfect kit to find your ideal size before purchasing the Oura Ring 4 Comes with a range of ring sizers of sizes 4-15, to know your correct finger measurement Choose the finger you plan to wear the Oura Ring 4 on (index, middle, or ring fingers are recommended for optimal performance and accuracy) Try on the plastic rings to find the size that fits comfortably and securely on the base of your finger Wear the ring sizer for at least 24 hours to confirm your best fit, as your finger will expand and contract based on your environment Oura Ring 4 sizes will differ slightly from standard ring sizes, so make sure not to assume your size without proper measurement Ring sizers are made from plastic mould and may feel less comfortable but the Oura rings (sold separately) will have a seamless inner moulding for comfort