Every major smart ring brand has the same sizing problem — standard jewelry sizing doesn’t translate cleanly to a ring built around internal sensors. Here’s how Oura, RingConn, and Ultrahuman each handle it. (For general sizing rules, see our Oura Ring size guide or reference the complete Oura Ring size chart).
Why This Comparison Matters
If you’re choosing between smart ring brands, sizing confusion isn’t unique to Oura — every major smart ring maker uses its own size scale that doesn’t map directly onto standard jewelry sizing, and all three of the brands compared here solve it the same basic way: a free physical sizing kit shipped before the ring itself. The differences are in size range, and in how each brand talks about the tradeoffs.
Understanding the nuances in an Oura vs RingConn vs Ultrahuman comparison helps highlight key sizing and feature variations.
Size Range and Sizing Kit Comparison
| Brand / Model | Size Range | Half Sizes | Sizing Kit | Recommended Finger |
| Oura Ring 5 | 6–13 (8 sizes) | None | Free, ships separately | Index (default) |
| Oura Ring 4 | 4–15 (12 sizes) | None | Free, ships separately | Index (default) |
| RingConn Gen 3 | 6–15 (10 sizes) | None | Free, ships separately | Index, middle, or ring |
| RingConn Gen 2 / Gen 2 Air | 6–14 (9 sizes) | None | Free, ships separately | Index, middle, or ring |
| Ultrahuman Ring AIR | 5–14 (10 sizes) | None | Free, ships separately | Index, middle, or ring |
Every brand here lands on the same core rule: no half sizes, and a free physical sizing kit that ships ahead of the actual ring. If you’re on the small end of the range, Ultrahuman’s size 5 floor is the lowest of the three; if you’re on the large end, RingConn Gen 3’s size 15 ceiling is the highest.
What’s Actually Different Between Them
The size ranges shift slightly, but the underlying sizing philosophy is nearly identical across all three brands: none of them trust standard ring sizing to translate accurately, because all three build sensor housings into the interior of the band, and none of them offer half sizes or post-purchase resizing. If you’ve read our main size guide, the reasoning covered there for Oura applies almost exactly to RingConn and Ultrahuman as well. Learn why Oura sizing is different from traditional jewelry.
Where they diverge more is finger recommendation flexibility — RingConn and Ultrahuman both explicitly recommend index, middle, or ring finger as roughly interchangeable options, while Oura’s own materials lean more specifically toward the index finger as the default. In practice, the underlying reason is the same across all three: pick a finger with relatively stable, low-movement positioning, and stay consistent about which one you use. Read about selecting the best finger for Oura Ring accuracy.
If You’re Comparing Rings Before Buying
Sizing alone shouldn’t determine whether you choose Oura, RingConn, or Ultrahuman (for a detailed comparison, see our Oura vs RingConn vs Ultrahuman guide). All three brands offer a way to confirm your ring size before purchase, so the more meaningful differences are their health features, subscription model, battery life, and app experience. Before ordering an Oura Ring, you can use the Oura Ring size guide to estimate your size, then verify it with Oura’s official sizing kit for the most accurate fit (or review a free vs paid sizing kit comparison).
If you’re switching from another smart ring brand, don’t assume your current size will transfer directly. Each manufacturer uses a different internal design and sizing system, so even if two rings share the same size number, they may fit differently. For the best results, use the Oura Ring size guide as a starting point and always confirm your fit with Oura’s official sizing kit before purchasing a new ring
Frequently Asked Questions
Do Oura, RingConn, and Ultrahuman use the same size scale?
No. Each brand has its own size range and its own physical sizing kit. A size 8 on one brand doesn’t necessarily correspond to a size 8 on another — always size separately for the specific ring you’re ordering.
Which smart ring brand has the widest size range?
Among the models compared here, RingConn Gen 3 covers the widest range at sizes 6 through 15. Ultrahuman Ring AIR covers 5 through 14, and Oura covers 4 through 15 across its two current generations combined (Ring 4: 4–15, Ring 5: 6–13).
Can I use one brand’s sizing kit to estimate another brand’s size?
Only as a rough starting reference, not a reliable final answer. Each brand’s ring has different interior geometry, so request the specific brand’s own free sizing kit before ordering rather than converting from another brand’s result.
Do any of these brands offer half sizes?
No — Oura, RingConn, and Ultrahuman all currently offer whole sizes only, which makes accurate initial measurement more important across all three, since there’s no in-between option to fall back on.
This guide is published by Oura Ring Size, an independent sizing resource not affiliated with, endorsed by, or sponsored by Oura Health Oy. “Oura” and “Oura Ring” are trademarks of Oura Health Oy, referenced here only to describe compatibility. Sizing details for RingConn and Ultrahuman are based on publicly available information from those brands as of this writing and may change — confirm current specifications directly with each brand before purchase.
