How to find your smart ring size for Oura, Galaxy Ring and Ultrahuman

Don't order a smart ring in your jewelry size. Oura, Ultrahuman and RingConn all say their sizes differ from standard ring sizes, Ultrahuman and RingConn add that they differ from other smart ring brands, and even a single brand can change sizing between models. Samsung says the Galaxy Ring follows US standard sizes, but it still recommends its kit. A ring that's too loose lets light leak past the sensors and leaves gaps in your data, Ultrahuman explains, while one that's too tight is uncomfortable to wear day and night.

Oura, Samsung, Ultrahuman and RingConn all send a free kit of sample rings before they ship the real one. This guide is based on each company's sizing instructions.

Size ranges and kits by brand

How to use a smart ring sizing kit

1. Order the ring with the sizing kit option. The kit ships first, and the ring follows after you confirm a size.
2. Pick a finger. Oura recommends the index finger for the most accurate readings and says the middle or ring finger also work. Avoid fingers where the knuckle is much wider than the base. Ultrahuman suggests trying the index, middle and ring fingers on both hands and skipping the thumb and little finger.
3. Put the sizer on the right way. The sensors belong on the palm side of the finger, and Ultrahuman tells you to wear its sizer with the size number facing your palm.
4. Check the fit. The ring should feel snug, not tight, at the base of your finger and shouldn't spin on its own. Ultrahuman says your skin should move with the ring when you twist it. Oura suggests making a fist: if you see a gap between the ring and the top of your finger, try a smaller size.
5. Wear it for a full day and night. Oura, Samsung and RingConn recommend at least 24 hours, and Oura and RingConn say to sleep in it. Ultrahuman asks for two nights, through morning, evening, a workout and sleep.
6. If you're between sizes, choose the smaller one. Oura and RingConn recommend it, and Ultrahuman says to pick the tighter size if both are comfortable, or the one that fits more than one finger.
7. Confirm your size where the brand asks: My Orders for Oura and RingConn, the My Order page for Samsung, or the Ultrahuman app, which you open by scanning the QR code in the kit.

Brand by brand

Oura

Kits are labeled by generation, and Oura says Ring 5 sizing differs slightly from Ring 4, so use the right one. The plastic sizers match the real ring's width and circumference but weigh less. Oura's online store doesn't sell kits on their own; some authorized retailers do, with a credit toward a ring. After you confirm, Oura says the ring usually leaves its warehouse within one to two days and arrives two to five business days after the shipping email. More on the current model in our Oura Ring guide.

Samsung Galaxy Ring

Samsung bases its sizes on US standard sizes and added 14 and 15 in January 2025. Enter your size within 14 days of receiving the kit or the order is canceled. You can keep the kit, and you get one per order no matter how many rings you buy. See our Galaxy Ring guide.

Ultrahuman

The kit has 10 sample rings in sizes 5 to 14. If you know your Ring Air size, Ultrahuman says the Ring Pro fits the same. The company says its most common sizes are 6 to 8 for women and 9 to 11 for men, with plenty of variation. Our Ultrahuman Ring Pro guide covers the ring itself.

RingConn

Gen 3 uses a different sizing system from earlier RingConn rings, so order the Gen 3 kit even if you've worn a RingConn before. RingConn says the kit takes three to eight days to arrive.

Circular

Circular recommends ordering its sizing kit first. If the Circular Ring 2 still doesn't fit, it can be returned within 14 days, with return shipping paid by the customer.

Why your size changes during the day

Ultrahuman lists temperature, fluid retention, activity and the menstrual cycle as reasons fingers swell or shrink, and notes that fingers tend to be a little larger in the morning and slimmer when your hands are cold. That's why the brands ask you to keep the sizer on for a day or more: a ring that feels right at your desk can pinch at 6 a.m. or slide around on a cold walk. If your fingers change size over time, Oura says you can move the ring to another finger or hand as long as it stays snug.

If the ring doesn't fit

Oura asks you to contact its Member Care team, and it allows one exchange per ring for a different size of the same model. Samsung lets you get a refund on the Galaxy Ring without returning the sizing kit. Circular accepts returns within 14 days. Check the policy before you confirm a size, because some brands allow only one return or exchange.