Measure Ring Size

Online ring sizer

Online ring sizer

You already own a ring that fits. Calibrate your screen with a bank card, place the ring flat on the display, and match the circle to the ring's inner edge.

Note: Dragging a circle over a ring does not, by itself, measure anything. This tool only shows a size after you calibrate against a real card — and it labels every result as estimated, not exact.

  1. Calibrate with a card

    Hold a standard bank card flat against the screen. Adjust the rectangle until its edges line up with the card's edges. A tilted card, or a card held away from the screen, will give a wrong size.

  2. Place the ring on the screen

    Lay the ring flat on the display, centred on the circle. The circle must follow the ring's inner edge — the hole you put your finger through — not the outer edge of the band.

  3. Adjust, then read the result

    Use the slider, the step buttons, or the fine 0.1 mm controls until the circle sits exactly on the inner edge. The diameter, circumference and sizes update as you adjust.

Card edges = rectangle edges

Dashed line: your card. Solid line: the rectangle. They must coincide.

Circle = inner edge, not outer band

The dark line is the measurement. The gold band is the ring itself.

Step 1 — Calibrate with a bank card

Step 1 of 2

Place a real bank card flat against the screen. Adjust the rectangle below until its edges line up with the card. The rectangle's height follows the card's proportions automatically, so matching the width also checks the height.

If the rectangle is wider than your screen, rotate to landscape or use a larger screen — do not guess the card's width.

No size is shown until you confirm calibration. Skipping calibration would produce a fabricated result, so the tool refuses to guess.

Reference: standard bank card, 85.60 mm × 53.98 mm (ISO/IEC 7810 ID-1). Dragging a circle over a ring without this step does not produce a measurement — the tool refuses to show a size until calibration is confirmed.

Step 2 — Match the circle to the ring's inner edge

Step 2 of 2

Note: Complete calibration above first. The circle below is a preview only — it is not a measurement until calibration is confirmed.

Diameter and circumference appear here once calibration is confirmed.

Enter a diameter in millimetres, then Apply. It must be inside the chart range (12–24 mm).

Highlight my country's size
Place the ring flat on the screen, centred on the circle. The circle must follow the inner edge — the hole — not the outer band. Keep the ring flat; tilting it changes the apparent diameter.
Three steps: hold a standard bank card flat against the screen, match the on-screen rectangle to it, then match the circle to a ring
How screen calibration works, step by step. The diagram is illustrative — the sizer above calibrates against your real card on your real screen, never against this picture.
Illustration of a ring with a diameter arrow across its inner edge
Illustration only — not a sizing template. Match the inner edge of a ring in the working sizer above, not in this picture.

Why you can trust this result

  • Calibration uses a standard bank card (85.6 mm wide, ISO/IEC 7810 ID-1) — a physical reference, not a guess about your screen.
  • Your measurement is calculated in your browser and is not sent to a server. There is no account, and analytics runs only if you consent to it.
  • Results are guidance, not a guarantee. For an expensive or hard-to-resize ring, confirm with a professional fitting.

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