Colmi R09 sizing: how to pick your size before you order

Measure the exact finger you'll wear the Colmi R09 on, then match its circumference to Colmi's chart. Colmi's guide sent me a size 11 that didn't fit my index finger, and the store only takes back unworn rings.

Measure the exact finger you’ll wear the Colmi R09 on, then match that circumference to Colmi’s sizing chart before you order. Do it twice, with a physical ring sizer if you can get one, because a wrong size is hard to undo: there’s no sizing kit, and Colmi’s own store only takes back rings that are unworn.

I learned this with my own $20 ring. I measured my index finger with Colmi’s sizing guide and ordered a size 11. It doesn’t go on my index finger on either hand. The ring ended up on my pinky with a silicone adjuster, and on two of the seven nights in my review it slid enough to log bad sleep data.

How I put this together

The first-hand part is my own R09, which I bought from AliExpress and wore for a week next to my Apple Watch Ultra. Everything else comes from Colmi’s US site, checked on November 6, 2026: the R09 product page, the sizing guide, the online ring sizer and the refund policy. I haven’t used Colmi’s online sizer, so I describe how it works and can’t vouch for its accuracy.

Step 1: pick the finger first

Choose the finger before you measure anything. Each finger is a different size, and a ring sized for one finger turns into a guess on another. My size 11 was meant for my index finger. On my pinky it fits loosely enough that a silicone adjuster can’t keep it from sliding at night, and a ring that slides loses skin contact.

Colmi’s product page doesn’t say which finger to use. Its advice is one line: choose “a fit that feels secure without pressure, especially for overnight wear.”

Step 2: measure that finger’s circumference

Colmi’s chart sizes the R09 by circumference and inner diameter. Circumference is the one you can measure on your own hand. Wrap a ring sizer or a strip of paper around the finger where the ring will sit, mark where it meets and read the length in millimeters.

Measure twice. My one data point is that measuring once with Colmi’s guide got me a ring that didn’t fit the finger I measured.

Step 3: match it to Colmi’s chart

Here is Colmi’s sizing chart as its US store publishes it. The millimeter columns are my conversions of Colmi’s inch and centimeter figures.

Three things on Colmi’s pages don’t line up, and they matter if you’re near an edge:

• Each range ends where the next one starts. A 60.0 mm finger is the top of size 8 and the bottom of size 9. Colmi doesn’t say which way to go when you land on a boundary, and I couldn’t confirm it anywhere else on its site.
• Size 13 has no row. The store’s size menu lists 7 to 13, but the chart stops at 12.
• The spec list disagrees with the menu. The product details say “US ring sizes 8-13,” while the size menu offers a 7.

If your measurement sits on a boundary or above size 12, measure again before you pick.

Step 4: or measure a ring you already own

Colmi’s free online ring sizer works from your screen with no camera. You calibrate it by holding a credit or debit card to the display and matching its 53.98 mm short edge between two lines. Then you place a rigid ring that already fits the finger you want and adjust the circle to its inner edge. Colmi says a ring with a similar band width gives the best result.

This only helps if you own a ring that fits the exact finger you plan to use. A ring from another finger gives you that finger’s size, which is the mistake from Step 1.

Step 5: check the return terms before you try it on

Colmi’s US store offers free US shipping and 30-day returns. Its refund policy says the item has to be “unworn or unused,” in its original packaging, with proof of purchase. It offers no direct exchange: you return the ring, wait for the return to be accepted and buy the new size separately. Sale items can’t be returned at all.

The policy doesn’t say whether trying a ring on counts as worn, so a ring you’ve slept in to test the fit may not qualify. Ask support@colmi.com before you wear it overnight. Marketplace sellers set their own terms, and mine came from AliExpress, so Colmi’s policy wouldn’t have covered it. On November 6, 2026 every size and color of the R09 showed as sold out at colmi.com at $59.98.

Don’t size up for the battery

Colmi lists a 14mAh battery for sizes below 11 and an 18mAh battery for size 11 and above. Size changes the battery, but a bigger ring on the wrong finger slides. On the nights mine slid, the data was wrong. In my use the size 11 already ran about a week on a charge with quick top-ups in its case while I showered.

FAQ

Does the Colmi R09 run small?

I can’t confirm that across buyers. My one data point: the size 11 that Colmi’s guide pointed me to doesn’t go on my index finger on either hand. Measure the finger you’ll wear it on, twice, before you trust the chart.

Does the Colmi R09 come with a sizing kit?

Mine didn’t. Colmi’s US product page lists the ring, a charging case, a charging cable and a quick start guide in the box, with no sizing kit. Colmi points buyers to its sizing chart and its free online ring sizer instead.

What sizes does the Colmi R09 come in?

Colmi’s US store menu lists sizes 7 to 13 in silver, gold and black. Its product details say 8 to 13, and its sizing chart covers only 7 to 12.

Can I exchange a Colmi R09 for another size?

Not directly at colmi.com. You request a return within 30 days of delivery, the ring has to be unworn or unused in its original packaging, and you buy the new size as a separate order. Sale items can’t be returned.

Which finger should I wear a smart ring on?

Colmi doesn’t say. Pick the finger you’ll keep it on every night and size for that one. My ring ended up on a finger it wasn’t sized for, and two nights of sleep data out of seven were wrong. For how the R09 compares with other rings and watches, see my best sleep tracker guide.