Smart Ring Sizing Kits
My attempt to get measurements of various smart ring sizing kit rings…
Pardon the mess on my workbench pad. I tried to clean it and after looking at the photos I realized I failed miserably.
I originally bought the Oura Ring 2 in size 12 in stealth black in July 2020. Then, two years later in July 2022 I bought an Oura Ring 3 in size 12 in stealth black. Now, in October 2024 I have preordered an Oura Ring 4 in size 12 in stealth black.
I noticed on Reddit that there are several people asking for size measurements of the various ring samples in the ring sizing kits. This article is my attempt to share those numbers.
NOTE: These measurements are subject to human error or horribly calibrated measurement devices. Also, these sizing kits are plastic and may not exactly 100% represent the actual rings.
ALSO: I have ordered UltraHuman Ring Air, Ring Conn and Oura Ring gen 3 sizing kits to expand on my measurements. I will update this article after I get each kit and measure the various sizes.
Oura Ring 4 sizing kit.
Oura Ring 2 sizing kit.
The green row above are the measurements for my Oura Ring 3 size 12 in stealth black. It is 2 years old, maybe no longer perfectly round and worn down. In my personal opinion, the Oura Ring 2 and 3 fit the same, but I am still measuring all the sizes in the Oura Ring 3 kit when I get it.
Samsung Galaxy Ring sizing kit.
The Galaxy Ring has sensor bumps on the inner wall of the ring (photo lower below), which causes similar measurement differences in Diameter to Bumps and the Ruler Size, like the Oura Ring 2 & 3.
UltraHuman Air Ring sizing kit.
One thing I have noticed is the UltraHuman Air Ring is about a size larger per ring than the other kits. You can see in my personal picks table below that I go down a size in pretty much each finger. The ruler measurements show the difference visibly.
RingConn Ring sizing kit.
Coming soon…
Here are some additional photos to help explain how the measurements were taken.
Full Diameter
When measuring the full inner diameter, I avoided having the caliper in or near a bump or the grooves used for aligning inside the charging base.
Diameter to Bump
The diameter to bump measurements were taken with my best attempt to measure from the inner wall on one side directly across from a interior bump on the opposite inner wall of the ring. Apologies I do not have a photo of this measurement method.
Ring Thickness
I avoided measuring the ring where a bump or groove was on the inner wall of the ring.
Ring Length
I believe with every ring, the opposing sides of the ring were both able to fit along the measuring surface of the caliper, as shown above. Even the Oura Ring 4 in size 15 fits as shown. I do think an Oura Ring of size 17 or larger would require me to get different calipers.
Ring on Ruler Size
NOTE: My ruler measurements are an estimate of where the centerline of the ring would fall on the ruler. I say “centerline” as that is where the bumps are on the rings. In the image above this is about 9.40 on this scale (red numbers). In the 1st image posted on this article, there is a cable with a bunch of metal rings on it. They are all full and half sizes, from 0 to 13. For clarity, the full size rings on that cable fall just fractionally above or on the line where the respective RED size number is positioned on this ruler (2nd photo below). My guess is the bumps on the inner wall of a given “Smart Ring” ring may prevent it from sliding fully to their approximate size.
Some readers may state that the ruler measurement should be taken from the edge closer to the higher number. As this may or is likely the part of the ring touching the ruler. I mostly agree with this assumption, for example with the Oura Ring 4 samples I measured. But, with the Oura Ring 2 samples, the inner bumps are so large, they prevent this scenario from happening. That all being said, none of the rings I measure had an edge that came near the rings marked size. Like shown in the image above, the Oura Ring 4 size 10 would measure 9.75 on the ruler on the largest touching side/edge. Below you can see the Oura Ring 2 size 10 would measure about 8.5 if measured at the same largest touching side/edge on the ruler.
In the image below, you can see the size 10 fitting ring from the cable falls just above the RED 10 make on the ruler. Other whole size fitting rings I tried did the same. You can see the -9 on the cable to the left and the -10 on the cable to the right, these are the 9.5 and 10.5 sizes respectively.
Oura Ring 4 sensor bumps
The tiny tiny bumps on the inside of this Oura Ring 4 have little to no impact on the fit. The Oura Ring 4 also has 2 alignment grooves in the inner wall of the ring. This allows the ring to properly align in the charging base.
Oura Ring 2 sensor bumps
In contrast, depending on the person and their fingers the bumps on the inside of this Oura Ring 2 (and 3) may have noticeable impact on the fit. The Oura Ring 2 (and 3) do not have alignment grooves in the inner wall of the ring (like the Oura Ring 4). The larger inner bumps are used to get the ring to align properly in the charging base.
Samsung Galaxy Ring sensor bumps
Visually the sensor bumps on the inside of the Galaxy Ring resemble those in the Oura Ring 2 & 3.
UltraHuman Air Ring sensor bumps
Visually the sensor bump on the inside of the UltraHuman Air Ring is a flat section unlike any of the other rings I have measured so far.
One thing I have noticed is the UltraHuman Air Ring is about a size larger per ring than the other kits. You can see in my personal picks tbale below that I go down a size in pretty much each finger. The ruler measurements show the difference visibly.
Because the UltraHuman Air RIng uses a flat sensor bump, the measurement position on the ring ruler changes when the sensor bump is on the rounded size of the ruler vs on the cutout section where the scale is.
RingConn Ring sensor bumps
Coming soon…
My personal subjective ring sizing picks
I live in a humid climate in the southeastern part of the USA. Depending on the time of year, temperature and humidity levels outside my hands and fingers swell a tiny bit. That being said, if I was to buy one of the smart rings above for one of those fingers listed, those are the sizes I would buy for long term all day comfort. I personally own and wear an Oura Ring size 12 ring on my left ring finger. The only finger above that may take a different size is my left index finger, which could take an Oura Ring size 12 in cooler and dryer climates.
Thanks for reading. As I get more smart ring sizing kits in, I will add to this article.
