3D Print Your Own Ultrahuman Ring Sizing Kit
Skip the wait for a sizing kit in the post. If you have access to a 3D printer, you can print accurate sizing rings at home and find your perfect fit in minutes — then order with 10% off.
· Files provided by Ultrahuman · Sizes 5–14
Why 3D print your sizing kit?
Getting your ring size right is the single most important step before ordering an Ultrahuman Ring. Ultrahuman offer a free physical sizing kit that ships to your door — but it takes a few days. If you have access to a 3D printer (or know someone who does), you can skip the wait entirely.
This is exactly how I found my size. I printed a few sizes on an SLA printer, tried them on, wore the best fit overnight, and had my size nailed down within 24 hours. It also means you can order your ring with confidence — and if you're on the fence about committing to an Ultrahuman Ring just yet, printing a sizing ring first costs you nothing but a few millilitres of resin.
How it works — five simple steps
1. Download the files
Grab the STL or STEP files below for the sizes you think you'll need. Not sure? Download the full ZIP with all sizes 5–14.
2. Print the rings
Import into your slicer and print at the highest resolution your printer supports. SLA/LCD/DLP printers give the best dimensional accuracy.
3. Try them on
Slide each ring onto the finger you plan to wear your Ultrahuman Ring on — typically the index or middle finger. You want a snug fit that doesn't pinch.
4. Wear overnight
Your fingers change size throughout the day. Wear your best-fitting ring overnight to make sure it's still comfortable when your fingers are at their largest (morning).
5. Order with confidence
Once you know your size, order your Ultrahuman Ring with 10% off — no more guessing.
Interactive 3D preview — Size 10
This is what the sizing ring looks like. Drag to rotate, scroll to zoom. The real print will be this exact geometry.
Sizing reference — inner diameters
These are the inner dimensions for each ring size, taken from Ultrahuman's official sizing drawings. Use them to verify the accuracy of your prints with a calliper.
| Size | Inner Diameter | Inner Circumference |
|---|---|---|
| 5 | 15.7 mm | 49.3 mm |
| 6 | 16.5 mm | 51.8 mm |
| 7 | 17.3 mm | 54.4 mm |
| 8 | 18.1 mm | 56.9 mm |
| 9 | 18.9 mm | 59.5 mm |
| 10 | 19.8 mm | 62.1 mm |
| 11 | 20.6 mm | 64.6 mm |
| 12 | 21.4 mm | 67.2 mm |
| 13 | 22.2 mm | 69.7 mm |
| 14 | 23.0 mm | 72.3 mm |
Download the files
Ultrahuman provide the sizing kit files in three formats. STL is the standard for 3D printing; STEP files are useful if you want to inspect or verify dimensions in CAD software before printing.
Complete Kit (All Sizes 5–14)
Contains STL files, STEP files and sizing drawings (PDF) · ~4.9 MB
Or download individual sizes in STL format:
15.7 mm Size 6
16.5 mm Size 7
17.3 mm Size 8
18.1 mm Size 9
18.9 mm Size 10
19.8 mm Size 11
20.6 mm Size 12
21.4 mm Size 13
22.2 mm Size 14
23.0 mm
Printing tips for the best accuracy
The accuracy of your printed sizing rings depends on your printer type, resolution and settings. Here is what works best:
Use an SLA/LCD/DLP printer
Resin printers produce much more dimensionally accurate prints than FDM for small parts like rings. If you only have access to an FDM printer it will still work — just print at the finest layer height your machine supports.
Print at maximum resolution
Set your slicer to the highest resolution (smallest layer height) available. For resin printers this is typically 0.025–0.05mm. Accuracy matters more than speed here.
Verify with a calliper
After printing, measure the inner diameter with digital callipers and compare against the sizing chart above. The STEP files include exact dimensions if you want to cross-reference in CAD software.
Don't have a 3D printer?
No problem — you have a few options. Ultrahuman ship a free physical sizing kit to your door, which takes a few days but costs nothing. You could also ask a friend, use a local makerspace, or try an online 3D printing service like Shapeways or Craftcloud — just upload the STL file and they'll post the printed ring to you.
Alternatively, if you already own a ring that fits the finger you plan to wear the Ultrahuman Ring on, measure its inner diameter and match it against the table above.
Ready to order?
Once you've found your size, you can order your Ultrahuman Ring AIR or Ring PRO with 10% off using our referral link. The discount applies automatically at checkout — no code to type. Not sure which ring? Check our Ring AIR vs Ring PRO comparison or read the full Ring AIR review.
Sizing kit — frequently asked questions
Can I really 3D print my own Ultrahuman sizing kit?
Yes. Ultrahuman officially provide the CAD files for exactly this purpose. The STL and STEP files on this page cover all available sizes (5–14) and are the same files hosted on Ultrahuman's own site.
What size Ultrahuman Ring should I get?
The best way to find out is to try sizing rings on your intended finger (typically index or middle) and wear one overnight. Your fingers swell in the morning, so a ring that feels fine in the afternoon might be tight at 7am. Print a couple of adjacent sizes and sleep with your best fit.
How accurate is a 3D printed sizing ring?
Very accurate on SLA/LCD/DLP printers at maximum resolution. FDM printers may have slightly more variance. Either way, use the STEP files and a set of digital callipers to verify the inner diameter against the sizing table above.
Which finger should I wear the Ultrahuman Ring on?
Ultrahuman recommend your index or middle finger for the most consistent sensor readings. Size accordingly — your index finger is usually a different size to your ring finger.
Can I order Ultrahuman's free sizing kit instead?
Absolutely. Ultrahuman ship a free physical sizing kit on request. It takes a few days to arrive but costs nothing. The 3D print option is for people who want to find their size immediately without waiting.
Does the 10% discount apply once I know my size?
Yes — the referral discount on this site gives you 10% off the Ring AIR, Ring PRO, Blood Vision and accessories. It applies automatically at checkout and works worldwide.