Why Wearing Your Oura Ring on the Wrong Finger Ruins Sleep & Heart Data

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Human fingers change volume throughout a normal 24-hour cycle. Peripheral blood pooling, sodium intake, and ambient room temperatures cause fingers to expand by roughly half a size overnight. A ring that slips on comfortably at noon can feel uncomfortably tight by 4:00 AM, tempting users to choose a larger size that fits too loosely during the day.

This daily swelling cycle makes the plastic sizing kit indispensable. Wear the sample ring for at least 24 consecutive hours on your target finger before confirming an order. Your ideal fit should slide smoothly over the knuckle when pulled with deliberate resistance, yet twist cleanly without pinching the skin. If morning swelling makes removal impossible without soap and water, the size is too small; if the sample spins freely when you wash your hands, optical tracking will fail at night.