Free online ring size calculator — calibrate once, then measure a ring or your finger. No download needed.
Step 1: Calibrate Your Screen
Place a standard credit card on your screen for pixel density calibration.
Place your ring on the screen and drag the handles to match its inner edge.
Your Ring Size
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US Size
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UK Size
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EU Size
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Japan Size
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Diameter (mm)
Tip: Calibrate your screen with a credit card first for maximum accuracy. Want saved sizes for family members and more features? Download the app.
A standard credit card is 85.6mm wide. Drag the handles to match your card's width exactly.