Ring Sizer: iRing is a ring size app for iPhone and iPad that helps you find your size before you buy online. Match a ring to a circle on the screen, or use the interactive finger sizer slider to measure your finger directly. As a ring sizer app for iPhone it needs no physical tools, only a one-time calibration: hold a ruler or a bank card against the screen and match the scale, because every device shows a slightly different physical size.

Once calibrated, results come within about half a size. That is good enough to order with confidence for yourself; for a surprise engagement ring, have a jeweller confirm it. Measure at the end of the day at normal room temperature, since fingers are smallest when cold and largest when warm, and a ring has to pass the knuckle on the worst day.

The ring size converter switches between US, UK, EU, Japan and other standards, both ways, and a full size chart can be read straight off. A short quiz gives a personal recommendation, and a finger guide explains which finger to measure and how sizes differ between hands. Measurement history lets you save and compare results over time.

Beyond sizing, iRing is a jewelry guide: 16 ring styles including solitaire, halo and eternity, a guide to 12 metals, an encyclopedia of 21 gemstones with a birthstone calendar, an interactive ring anatomy and care tips for different metals and gems. It works offline with no account and no sign-up.

The core app includes the main sizing features. An optional Premium upgrade adds the rest of the experience.