Why it is accurate
Most ring sizer apps draw a circle using the pixel density your phone reports to the system. On many devices that value is a factory default and can be off by 10–20%, which turns into an error of two or more ring sizes. Ring Sizer asks you to place any bank card (ISO ID‑1, 85.60 × 53.98 mm) on the screen once and measures the real size of your display. Every circle and ruler after that is drawn in true millimetres.
Measure a ring
Place a ring you already own on the screen and match the circle to its inner edge. Fine‑tune in 0.05 mm steps with a magnified view.
Measure a finger
No ring? Wrap a strip of paper around your finger, mark the overlap and lay it on the on‑screen ruler.
Ring size chart & converter
Convert between US, UK, EU/ISO, Italian/Swiss, Japanese, Chinese and Indian sizes, diameter and circumference. Works offline.
Save & share
Keep sizes for yourself and for people you buy gifts for. Share a result as text in one tap. Everything stays on your device.
Respectful by design
- One optional ad after your result, never before it. Remove ads forever with a single one‑time purchase.
- No camera, no photos of your cards or hands. The app never asks for camera permission.
- No account, no cloud. Your sizes are stored only on your phone.
- Dark and light themes, tablet support.
Questions?
See the support page or write to [email protected].