Smart ring sizing compared: is RingConn sizing the same as Oura?

The honest answer: no official equivalence exists

If you own an Oura and you're eyeing a RingConn, or the other way around, the obvious shortcut is to order the same number. Don't. We read the sizing pages of every ring we cover, and not one brand says its sizes line up with another brand's. Several say the opposite in writing. RingConn's Gen 3 page is the bluntest: “RingConn Gen 3 ring sizes differ from other RingConn rings, standard rings and other smart ring brands” (RingConn). Oura says its whole sizes “differ slightly from standard US ring sizes, so it's important to test with our sizers even if you know your usual ring size” ( Oura Support).

So the straight answer to “is RingConn sizing the same as Oura?” is that nobody has said so, and RingConn has said the reverse. Your Oura size and your RingConn size may turn out to be the same number on your finger. That's a coincidence you can't plan around, because neither brand publishes a conversion chart you could check it against.

Why would two size 10s fit differently? Oura gives the clearest clue about its own rings: Ring 5's “redesigned interior fits differently than Oura Ring 4” ( Oura sizing page). If a new interior shape changes the fit inside one brand, there's no reason to expect two different brands' interiors to match. That's our reading of the evidence, not a measurement, but every brand's own advice points the same way: use its sizer. The rest of our battery and sizing hub follows the same rule.

What each brand says about its own sizing

Here is every relevant line we found, quoted from the brand's own pages. Read them together and one pattern stands out: every brand points you to its own sizer, and none points you to anyone else's chart.

Notice what's missing. Nobody says “our 9 equals Oura's 9.” RingConn and Ultrahuman explicitly say their sizing differs from other smart rings. Oura, Samsung and Circular say theirs differs from standard jewelry sizes. A kit from one brand tells you nothing reliable about another brand's ring.

Size ranges and sizing kits, side by side

Every ring we cover, with its published size range and how its maker handles sizing. Each cell links to the page it came from.

The widest range belongs to the Oura Ring 4 (4 to 15), followed by the Samsung Galaxy Ring (5 to 15) and the RingConn Gen 3 (6 to 15). The narrowest is Oura's current ring, the Ring 5, at 6 to 13. If you sit at either end of the scale, our guide to smart rings in large and small sizes ranks the rings by which sizes they actually make.

One warning about reading that table: a range is not a conversion. “Size 10” is a label inside one brand's system. A RingConn 10 and a Galaxy Ring 10 are two different rings made to two different specs, and neither maker has told us how they compare.

The kits themselves differ in ways that matter to your wallet and your patience:

• Oura: free on Oura's own store. Android Police reported that the Ring 5 kit on Amazon comes with a matching Amazon credit toward the ring (Android Police). Ring 5 and Ring 4 use separate kits.
• RingConn: complimentary, and for Gen 3 the ring ships after you confirm your size.
• Samsung: complimentary. Choose the “I don't know my size” option and the kit ships first. One catch: Samsung's US page says its kit is “now including two new sizes,” yet the same page still says “The sample rings come in 9 sizes, from 5 to 13” ( Samsung US). If you need a 14 or 15, confirm your kit includes them.
• Ultrahuman: a free kit with a Ring PRO order that Ultrahuman says needs no return. A Ring PRO kit covering sizes 5 to 14 is also listed on Amazon, even though the ring itself isn't.
• Circular: a replica-ring kit as a paid add-on at checkout, or a printable guide. Circular's help page says sizing kits “are consumables that are not refundable.”

Same brand, different generation, different fit

Brand loyalty doesn't save you from re-sizing either. Two of the four big brands say outright that their own generations fit differently.

Oura Ring 5 vs Oura Ring 4

Oura says Ring 5's interior “fits differently than Oura Ring 4,” and it sells separate sizing kits: Ring 5 sizers run 6 to 13, Ring 4 sizers 4 to 15. If you're upgrading from a Ring 4, your old size is a starting guess at best. Order the Ring 5 kit. The size change is one of several differences we cover in Oura Ring 4 vs Ring 5, alongside the membership both rings need.

RingConn Gen 3 vs Gen 2 and Gen 2 Air

RingConn Gen 3 sizes differ from “other RingConn rings.” Gen 2 and Gen 2 Air are the exception that proves the point: RingConn says “The ring sizes for both Gen 2 and Gen 2 Air are the same” (RingConn Gen 2 Air page). So a Gen 2 owner can buy a Gen 2 Air in the same size, but not a Gen 3. Our RingConn Gen 3 vs Gen 2 comparison covers what else changed.

Ultrahuman Ring AIR vs Ring PRO

Ultrahuman's Ring AIR FAQ says an owner of its earlier R1 “will find the Ring AIR will fit you just the same.” We found no matching statement about Ring AIR sizes carrying over to the Ring PRO, which is the only Ultrahuman ring sold in the US right now (the Ring AIR isn't). Treat the PRO as a fresh sizing job.

Samsung Galaxy Ring

There's only one Galaxy Ring model so far, so no generation question yet. Samsung added sizes 14 and 15 in January 2025, bringing the range to 5 through 15 (Samsung Newsroom).

Circular: the ring that runs half a size large

Circular is the one brand that relates its sizes to standard jewelry sizes at all, and even that is approximate. Its shop page says its US sizes 6 to 14 “run about half a size above standard,” and it offers a printable sizing guide alongside the replica-ring kit. The practical result: a Circular size is not your jewelry size, and it's not an Oura or RingConn size either. Use Circular's replica rings or its guide, and remember the kit isn't refundable. The Circular Ring 2 is also sold only from Circular's own store, so its 14-day return window, not Amazon's, is your safety net. Our Circular Ring 2 review has the rest of the fine print.

What to look for in a brand's sizing process

Since you can't carry a size between brands, the sizing process itself becomes part of what you're buying. Here's what separates a good one from a gamble:

1. A physical kit for the exact model and generation. Oura's Ring 5 kit won't size a Ring 4, and RingConn's Gen 3 kit is specific to Gen 3.
2. Kit first, ring second. RingConn (Gen 3) and Samsung ship the kit before the ring and wait for you to confirm. That order of operations is what prevents a wrong-size ring from ever shipping.
3. Coverage at the ends of the range. If you need the smallest or largest size, check that the kit actually includes it (see Samsung's mixed messaging above).
4. What the kit costs you. Free on Oura's, RingConn's, Samsung's and Ultrahuman's own stores; a non-refundable add-on at Circular.
5. A return window on the ring. If the size still turns out wrong, the store you bought from decides what happens next. Our warranty and returns guide compares the policies.

Switching brands: a step-by-step plan

Moving from Oura to a no-fee ring is the most common switch we write about, since it's how you drop the membership. Our best smart rings without a subscription covers which ring to switch to. Here's how to get the size right when you do:

1. Forget your old number. Your Oura size, your RingConn size and your jewelry size are three different measurements. None transfers.
2. Pick your finger first. Oura recommends the index finger for best accuracy; RingConn recommends the index, middle or ring finger. Size the finger you'll actually wear it on. Our guide on which finger to wear a smart ring on goes deeper.
3. Order the new brand's kit for the exact model. Not a generic plastic sizer, not a jeweler's mandrel.
4. Wear the sizer for a full day and a night. Oura says to “Wear the sizer for a full day, including while you sleep,” and Samsung recommends keeping its sample ring on “for over 24 hours” because “Finger sizes can change from day to night.”
5. Do Oura's fist test. “Make a fist. If you see a gap between the ring and the top of your finger, try a smaller size.” The target, in Oura's words, is “snug, not tight.” The test works with any brand's sizer.
6. Confirm, then order. Keep the sizer until the real ring arrives and fits, so you can recheck if something feels off.

For the full measuring method, including what to do between sizes, see our smart ring sizing guide.

Sizing mistakes that cost a return

• Ordering your Oura size in a RingConn, or the reverse. No brand supports it, and RingConn explicitly says its sizes differ from other brands.
• Upgrading within a brand on autopilot. Oura Ring 4 to Ring 5 and RingConn Gen 2 to Gen 3 both change the fit, by the brands' own statements.
• Using a jewelry-store size. Oura, Samsung and RingConn all say their sizes differ from standard rings, and Circular runs about half a size above standard.
• Sizing in the morning only. Fingers change through the day and night; that's why Oura and Samsung both ask for a full 24 hours with the sizer.
• Assuming the kit covers your size. At the ends of a range, check before you order. If you need a 4, the Oura Ring 4 is the only ring we cover that comes in one.
• Sizing one finger and wearing another. A size fits a finger, not a person.

Weighing Oura against RingConn on more than fit? Our Oura vs RingConn comparison puts the three-year cost next to the accuracy evidence.