RingSizer – Ring Size Tool

RingSizer turns your iPhone into a precision jeweler's tool — no ring sizer, no guesswork, no trip to the store. MEASURE YOUR RING Already have a ring that fits? Place it flat on your screen and align it with the on-screen guide. RingSizer uses your device's exact screen dimensions — with optional bank-card calibration for extra precision — to calculate your true size. MEASURE YOUR FINGER No ring on hand? Use the two-step Ellipse Method. Fingers aren't perfectly round, so RingSizer measures both width and thickness for a scientifically accurate fit, based on the same math jewelers use. CONVERT BETWEEN SYSTEMS Instantly convert between EU, US, UK, Japanese, Australian and Swiss/German ring sizes — or look up any size by diameter and circumference. LIFE-SIZE RULER A true-to-scale on-screen ruler for measuring anything small, in mm, cm or inches. FEATURES • High-accuracy ellipse-based finger measurement • Bank-card screen calibration for pixel-perfect results • Worldwide size conversion (EU, US, UK, JP, AU, CH/DE) • Save and organize your measurement history • Evening measurement reminder — fingers swell throughout the day, so a second reading helps you land on your truest size • Private by design — your measurements never leave your device RingSizer Premium unlocks unlimited history, expert fitting advice, and full worldwide size conversion — with a one-time purchase, no subscription. Whether you're buying a ring as a surprise, replacing a lost one, or shopping online, RingSizer gives you a confident, accurate answer in seconds.