Use the sizing kit made for the Oura Ring generation you plan to buy, then wear your best-fitting sizer for at least 24 hours—including overnight. The right size sits securely at the base of your finger and keeps the sensors in contact with your skin without feeling tight or causing discomfort.
1. Use the sizing kit for your Oura Ring generation
Oura sizes differ slightly from standard US ring sizes, and sizing varies between Oura generations. There are no half sizes, so do not rely on a jewelry ring or carry a size over from another Oura model. Try the sizing kit for your Oura Ring generation.
Oura’s guide, last updated August 10, 2026, lists sizers from sizes 4–15 for Oura Ring 4 and sizes 6–13 for Oura Ring 5. Those ranges apply to those models; they should not be assumed for other generations.
Oura says individual kits are not sold through its online store. A complimentary kit is included when you choose “Size Later” with a ring purchase. Many authorized retailers sell kits separately, and a kit purchase may qualify for credit toward a ring from that retailer.
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- SIZE BEFORE YOU BUY - It’s important to size yourself using our Oura Ring 5 Sizing Kit before purchasing an Oura Ring 5. Oura Ring 5 sizes are different from standard ring sizes and Oura Ring 4 sizes
- AVAILABLE SIZES - Oura Ring 5 is available in sizes 6-13. There are no half sizes
- CHOOSE A FINGER - Oura Ring 5 works on all fingers and can be worn on either hand. For optimal accuracy, we recommend wearing your Oura Ring 5 on your index, middle, or ring finger. Size the exact finger you plan to wear your Oura Ring on
- CHOOSE A FINGER - Oura Ring 5 works on all fingers and can be worn on either hand. For optimal accuracy, we recommend wearing your Oura Ring 5 on your index, middle, or ring finger. Size the exact finger you plan to wear your Oura Ring on
- COMFORT AND ACCURACY - A properly fitting Oura Ring 5 will result in the highest data accuracy, comfort, and overall experience
2. Compare fingers and hands
Oura says any finger can work, but recommends the index finger for best accuracy. The middle and ring fingers are also good options for signal quality. Try more than one finger, including on both hands, because fit can differ.
Choose a finger where the sizer rests securely at the base without an uncomfortable struggle over the knuckle. If the knuckle is much wider than the base and makes the sizer difficult to remove or fit securely, compare another finger.
Rank #2
- OURA RING 4 SIZING KIT - The Oura Ring 4 Sizing Kit is the ideal way to find the perfect size. It’s a custom sizer that allows for you, and those around you, to find the perfect fit before purchasing
- SIZE BEFORE YOU BUY - Oura Ring 4 sizes are different from standard ring sizes. Size yourself with the Oura Ring 4 Sizing Kit. For additional details, see “From the brand” section below
- NOT STANDARD SIZING - Oura Ring 4 sizes are slightly different from standard ring sizes, so it is important to size yourself using our Oura Ring 4 Sizing Kit. Oura Ring 4 is available in sizes 4-15. There are no half sizes
- COMFORT AND ACCURACY - A properly fitting Oura Ring will result in the highest data accuracy, comfort, and overall experience
- CHOOSE A FINGER - Oura Ring 4 works on all fingers and can be worn on either hand. For optimal accuracy, we recommend wearing your Oura Ring 4 on your index, middle, or ring finger. Size the exact finger you plan to wear your Oura Ring 4 on
3. Wear the sizer for a full day and night
Do not decide from a quick try-on. Finger size changes during the day and night, so wear the candidate sizer for at least 24 hours, including while sleeping and during normal activity. This helps you judge the fit across ordinary changes rather than at just one moment.
4. Check for secure contact without pressure
Oura’s fit guidance is: “For a proper fit, your ring should be snug but comfortable—not too tight or too loose.” The sizer should sit securely at the base and maintain contact with your skin. Make a fist: if there is a gap at the top, try a smaller size.
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Rank #3
- GIVE THE GIFT OF OURA RING 5 - This gifting kit takes the guesswork out of gifting, allowing the recipient to purchase the correct size and preferred finish of their Oura Ring 5 (Gift card sold separately)
- A FEW EASY STEPS - Purchase the gifting kit and an Amazon gift card with your desired value. Your friend or loved one will size themselves, and then purchase their Oura Ring 5 using the gift card
- WEAR TEST - Fingers expand and contract based on environmental factors, so we recommend wearing the ring sizer for 24 hours to confirm your best fit. The sizer ring should not rotate as you go about normal daily tasks
A plastic sizer may feel stickier than the finished ring. Even so, do not choose a size that causes ongoing pressure, pain, numbness, pinching, or marks that do not fade shortly after you remove it. If you notice these signs, try another size or finger rather than accepting an uncomfortable fit. See Oura’s Product Safety & Use guidance.
5. If you are between sizes
Oura recommends choosing the smaller size when two seem possible, because a more secure fit supports close sensor contact. Make that choice only if the smaller sizer remains comfortable during the full-day-and-night test. Comfort and a secure fit both matter; a size that feels restrictive is not a suitable choice.
Rank #4
- OURA RING GEN3 SIZING KIT - The Oura Ring Gen3 Sizing Kit is the ideal way to find the perfect size. It’s a custom sizer that allows for you, and those around you, to find the ideal fit before purchasing
- SIZE BEFORE YOU BUY – Size with Gen3 Sizing Kit prior to purchasing Oura Ring Gen3 (different sizing from Oura Ring 4). For additional details, see “From the brand” section below.
- NOT STANDARD SIZING — Oura Ring Gen3 Sizing Kit only works to size for Oura Ring Gen3. Gen3 sizes are different from standard ring sizes. Oura Ring Gen3 is available in sizes 6-13. There are no half sizes.
- HOW IT SHOULD FIT - We recommend wearing your ring sizer for at least 24 hours to confirm your best fit. Oura Ring Gen3 should fit securely and comfortably at the base of your finger. Your ring should not rotate as you go about normal daily tasks.
- COMFORT AND ACCURACY — A properly fitting Oura Ring Gen3 will result in the highest data accuracy, comfort, and overall experience
6. Confirm your size through the right purchase channel
After settling on a size, follow the confirmation instructions for where you bought the ring. Oura’s guide says online-store customers confirm through My Orders. If you bought a kit from an authorized retailer, return to that retailer to purchase the ring.
Some retailers, including Best Buy and Target, allow shoppers to try a sizing kit in person, according to Oura’s retail article, updated September 3, 2026. Oura gives Amazon as an example of a retailer where kit credit may appear as a coupon code. In-store access, stock, and credit terms vary by region and seller, so check the current offer before relying on them: Oura retail purchase information.
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- GIVE THE GIFT OF OURA RING 4 - This gifting kit takes the guesswork out of gifting, allowing the recipient to purchase the correct size and preferred finish of their Oura Ring 4. Gift card sold separately.
- A FEW EASY STEPS - Purchase the gifting kit and a gift card with your desired value. Your friend or loved one will size themselves, and then purchase their Oura Ring 4 using the gift card.
- CHOOSE A FINGER - Oura Ring 4 works on all fingers. Make sure to size the finger you plan to wear your Oura Ring on. For optimal performance and accuracy, we recommend wearing your Oura Ring on your index, middle, or ring finger.
- FIND YOUR FIT - Oura Ring 4 should fit snug around the base of your finger, but not to the point where it’s uncomfortable. When sizing yourself, the ring must fit over the largest part of your finger, like your knuckle.
- WEAR TEST - Your fingers expand and contract based on environmental factors, so we recommend wearing your ring sizer for 24 hours to confirm your best fit. Your ring should not rotate as you go about normal daily tasks.
7. Wear the ring in the correct orientation
Once you have the ring, orientation depends on the model. Oura says Ring 5, Ring 4, and Gen3 Horizon should be worn with the dimple facing the palm side. Gen3 Heritage should be worn with its flat side on top. See Oura’s ring sizing and wearing guidance.
What a snug fit can—and cannot—tell you about accuracy
Oura’s guidance connects close sensor contact with consistent data, which is why a secure, comfortable fit matters. The official material cited here does not quantify how much accuracy changes with ring size, so there is no supported percentage or independent measurement to apply. Use the fit checks and generation-matched sizer rather than treating a particular size as a guarantee of accuracy.
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