サイズガイド • 読了時間 約5分
スマートリングのサイズ選びガイド：Oura Ring 3/4・Galaxy Ring・Ultrahuman
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著者： Dhruv
2026年6月12日
Smart rings like the Oura Ring Gen 3 and Gen 4, Samsung Galaxy Ring, and Ultrahuman Ring Air have revolutionized personal biometric tracking. However, sizing a smart ring is fundamentally different from sizing a traditional gold or platinum wedding band.
Smart rings contain internal sensors, photoplethysmography (PPG) infrared modules, and battery enclosures that create inner surface bumps and require constant, intimate contact with your skin.
Why Standard Jewelry Ring Sizes Do Not Apply to Smart Rings
1.
Internal Sensor Bumps: Smart rings have small protruding sensor domes on the interior. These bumps push against the skin to maintain accurate optical blood flow readings, making them feel tighter than smooth metal bands.
2.
Different Finger Placements: Unlike wedding rings (which sit on the left ring finger), smart rings are optimized for the index finger or middle finger, which have stronger capillary blood flow and provide higher sensor fidelity.
3.
No Resizing Possible: Because smart rings are packed with micro-electronics, lithium batteries, and resin coatings, they can never be resized.
Which Finger Should You Wear a Smart Ring On?
- Index Finger (Recommended by Oura & Samsung): Delivers the highest biometric accuracy for sleep, heart rate, and temperature tracking due to palm vasculature.
- Middle Finger (Most Comfortable for Many): Great balance between sensor contact and daily comfort when typing or working out.
- Ring Finger: Acceptable, but may provide slightly weaker pulse signals if the ring rotates during sleep.
Smart Ring Sizing Kit Comparison
| Feature | Oura Ring Gen 3/4 | Samsung Galaxy Ring | Ultrahuman Ring Air |
|---|---|---|---|
| Available Sizes | US 6 – 13 (Full sizes only) | US 5 – 13 (Full sizes only) | US 5 – 14 (Full sizes only) |
| Interior Profile | Domed sensor bumps | Concave aero design | Smooth inner epoxy resin |
| Sizing Kit Material | Matte plastic sizers | Molded resin shells | Sizing rings with dummy weight |
| Recommended Test Period | 24 Hours continuous | 24 Hours continuous | 24 Hours continuous |
The 24-Hour Wear Test Protocol
Because fingers swell during sleep and contract during cool daytime weather, follow this protocol before locking in your smart ring order:
1.
Wear the plastic sizing test ring on your target finger for a full 24 hours.
2.
Sleep with the test ring on to ensure it does not cut off circulation during nighttime swelling.
3.
Wash your hands with soap. The ring should not slide off effortlessly when wet, but should come off with a gentle twist over the knuckle.
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