The Edit — Gadgets
Smart Ring Sizing: Why Your Ring Size Is Wrong
Oura sells whole sizes only, they differ from standard US ring sizes, and a Ring 4 sizer does not size a Ring 5. How to use a sizing kit, which finger to choose, and how to buy one as a gift.
This guide is research-led: we have not handled these units ourselves. If you buy through our links we may earn a commission — it never changes a pick. How we choose
This page reads the leading maker’s own sizing guidance and 3 sizing options against what owners report, as How we choose describes. Nothing here was worn or tested.
Good fit Anyone buying, or gifting, a Ring 5
Not for Sizing a Ring 4, or a finger above size 13
Good fit A Ring 4 buyer, or a finger outside sizes 6 to 13
Not for Sizing a Ring 5
Samsung Galaxy Ring, size-first kit
Good fit A buyer who wants sizing built into the order
Not for Anyone who needs accurate sleep tracking
Smart ring sizes are not jewellery sizes
Oura sells whole sizes only, with no halves, and says its sizes differ slightly from standard US ring sizes. A jeweller’s 7 is therefore a guess at an Oura 7, not a match.
A smart ring is also built differently from a band of gold. The Oura Ring 5 is 6.09 mm wide and 2.28 mm thick by Oura’s figures, with sensor domes on the inside that need to sit against the skin. A ring that spins or lifts reads less well.
The index finger gives Oura its best readings
Oura says you can wear its ring on any finger, and recommends the index finger for the best accuracy. Its Ring 5 launch post names 3 that work: index, middle and ring. Avoid a finger whose knuckle is much wider than its base, because a ring that fits over the knuckle will be loose below it.
The fit test is a fist. Oura says the ring should feel snug, not tight, and sit at the base of the finger. If you can see a gap between the ring and the top of your finger when you make a fist, try a smaller size.
Wear the sizer for 24 hours, including a night
Fingers change size through the day and night. Oura asks buyers to wear the sizer for a full day, sleep included, so the size still feels right in a warm bed and a cold morning.
A size that is perfect at 10 a.m. can pinch at midnight. Oura also suggests trying the sizers on both hands and on other fingers, and taking the most comfortable fit.
Each generation needs its own kit
Oura says sizing differs slightly between generations and labels each kit with the generation it fits. The Ring 5 kit runs from size 6 to 13. The Ring 4 kit runs from 4 to 15, so a finger outside 6 to 13 has a Ring 4 size and no Ring 5 size.
Oura Ring 5 Sizing Kit
974 ratings at 4.6, white plastic sizers in whole sizes 6 to 13, for the Ring 5 only.
Current price shown on Amazon. We may earn a commission.
| Fits | Oura Ring 5 |
|---|---|
| Sizes | 6 to 13, whole sizes |
974 ratings at 4.6. Owners call it essential before buying and say it makes the choice easy. Accuracy splits them: some found the right size at once, and some say the size 12 sizer ran small. Several found the fit too snug on the index finger and moved fingers.
Buy it if
- Anyone buying, or gifting, a Ring 5
Don't buy it if
- Sizing a Ring 4, or a finger above size 13
Oura Ring 4 Sizing Kit
4,079 ratings at 4.5, sizers in whole sizes 4 to 15, for the Ring 4 only.
Current price shown on Amazon. We may earn a commission.
| Fits | Oura Ring 4 |
|---|---|
| Sizes | 4 to 15, whole sizes |
4,079 ratings at 4.5. Owners find it helpful and accurate, and comfortable to wear for the day. Fit splits them, with some finding their size too big once the ring arrived. Value draws the same split, so buy it only for a Ring 4.
Buy it if
- A Ring 4 buyer, or a finger outside sizes 6 to 13
Don't buy it if
- Sizing a Ring 5
For a gift, give the sizing kit first
A smart ring is the hardest gadget to buy for someone else, because the one number you need is the one you cannot ask for without spoiling it. Samsung’s Galaxy Ring listing builds the answer in: the sizing kit ships before the ring.
Samsung Galaxy Ring, size-first kit
1,502 ratings at 3.0, sold with a sizing kit that ships before the ring.
Current price shown on Amazon. We may earn a commission.
| Sizing | Kit ships first, ring after |
|---|
1,502 ratings at 3.0. Owners like its looks and say it pairs smoothly with Samsung phones. Sleep tracking and value split them, and many call it a waste of money, so the size-first order is the best part of the purchase.
Buy it if
- A buyer who wants sizing built into the order
Don't buy it if
- Anyone who needs accurate sleep tracking
Smart rings compared ranks 6 rings and sets out which need a membership. For another gift that depends on the recipient’s phone, Bluetooth trackers explains the iPhone and Android split.