We may earn a commission from links on this page.Ive always preferred to wear my Oura ring on my ring finger. The company says that for optimal performance and accuracy, its best to wear it on your index finger, but that any finger can work. And if you ask longtime Oura users, youll get a variety of opinions. Does it really matter which finger you use? I realized I have the perfect way to test thisI have two gen 3 rings that fit my index and my ring fingers. I wore both for nearly two weeks to compare their readings and answer the question once and for all. Oura Ring 4 $349.00 at Amazon Get Deal Get Deal $349.00 at Amazon How I set up my experimentAs I explained in my four-year retrospective, Ive worn quite a few Oura rings over the years. My current unit is a gen 3 ring (the slightly older model) that I wear on my ring finger. I also had a gen 3 that fit my index finger, so I could wear both to bed for a few days and compare their readings.I actually wore three rings, but left one of them off my results because it turned out to be redundant. This one was a duplicate of the one I had on my ring finger, so I wore it on the other hands ring finger. It was a nearly-dead one that I had replaced when its battery wore out. It still had just enough juice to make it through each nights sleep so long as I charged it the next day. The readings were pretty much the same as my other ring finger, though, so I left this data off my results chart for claritys sake.For this experiment, I needed to pair each ring to a different account on a different phone. The things I do for you, dear readers. Since the accounts were all working from different (or nonexistent) baseline data, I avoided any scores that the app calculates based on your personal history. I stuck with readings like resting heart rate, heart rate variability, and sleep time. The one score I kept was sleep efficiency, since that combines multiple measurements from the same night.My results Credit: Beth Skwarecki Ive always felt like my ring finger readings are as good as my index finger readings, but now I have data to prove it. Look at these charts! The readings are often identical, and always close.There was one day where the two readings differedit's the very last day, with different respiratory rates and sleep efficiency. On that day, my second ring-finger ring (data not shown) matched the other ring-finger ring, suggesting that it's the index finger that was the outlier. Overall, the different fingers give readings that are much closer to each other than the different devices from this comparison (for that experiment, I wore Oura, Garmin, Whoop, Apple, and Fitbit devices at the same time).Any of the three placements I used would be perfectly good for daily wear. So why does Oura say your index finger is best? I reached out to the company for more information.What Oura saysThe gen 3 and 4 Oura rings work on any finger, an Oura spokesperson told me by email, so long as the ring fits tightly and securely around the base of the finger. So why the preference for the index finger? It turns out thats the finger where most people have the easiest time getting a good fit.Specifically: We suggest avoiding fingers with large knuckles where the base is significantly narrower, which can affect fit and sensor contact. This is why we generally recommend the index finger. If thats not comfortable or preferred, the middle or ring finger are also good alternatives. All three fingers have larger blood vessels, which help optimize PPG pulse monitoring. (PPG refers to photoplethysmography, the optical sensor system that picks up your pulse from your finger.)So if your ring finger has a big bony knuckle, youll need a larger size ring to get over the knuckle, and that ring wont be able to sit snugly against the base of your finger. I have no problem getting a secure fit on my ring finger, but I can see that my thumb has a large enough knuckle it probably wouldnt work well with the ring.Another issue with sizing is that the Oura ring doesnt come in half sizes, so you may not be able to find the perfect size for your preferred finger. That said, the gen 3 rings feel about a half-size smaller than the gen 4 rings at the same numbered size, so playing around with both sizing kits may help you to find the perfect fit if youre not picky about which version of the ring you end up with.