Ring Measurement Chart Online

Measure a ring right on your screen. First, calibrate by holding any standard bank or ID card against the on-screen card and dragging the slider until they match — this tells the tool how big a millimetre is on your display. Then lay a ring that fits flat on the screen and adjust the circle until it lines up with the ring’s inside edge. The tool reads the diameter and converts it to ring sizes worldwide.

Why calibrate first

Screens come in every size and pixel density, so a circle that is 17 mm across on one phone might be 12 mm or 25 mm on another. The calibration step fixes this: a standard payment or ID card is exactly 85.60 × 53.98 mm (the ISO/IEC 7810 ID-1 size) worldwide, so matching the on-screen card to a real one tells the tool how many screen pixels make a millimetre. Your calibration is remembered in this browser, so you only need to do it once per device.

How to measure a ring on screen

1. Turn up the screen brightness and lay the device flat.
2. Calibrate with a card: line up the left edge, then drag the slider until the right edge matches.
3. Place a ring that fits the intended finger flat on the circle.
4. Adjust the diameter until the circle fills the ring up to its inside edge — no gap and no overlap.
5. Read the size. If it falls between sizes, choose the larger one for a comfortable fit.
6. Repeat with a second ring if you have one, as a check.

Ring measurement chart

Each whole US size adds about 0.81 mm to the inside diameter and about 2.55 mm to the circumference. Half sizes sit midway.

Measuring the finger instead

If you don’t have a ring, wrap a strip of paper or thin string around the base of the finger, mark where it overlaps and measure the length in millimetres against a ruler. That is the circumference: divide by 3.1416 for the diameter, then enter it in the tool or read it from the chart. Make it snug but able to slide over the knuckle, and measure at the end of the day when fingers are largest.

Accuracy tips

• Calibrate carefully — a 2% calibration error changes the reading by about a quarter size.
• Look straight down at the screen, not at an angle.
• Measure the inside of the ring, not the outside edge.
• Thick or wide bands fit tighter; add a quarter to half a size for bands 6 mm or wider.
• Screen protectors and curved screen edges can distort; use the flat middle of the screen.
• For engagement rings or expensive pieces, confirm with a jeweller.

Worked example

On a laptop, the card matches the on-screen card at 323 pixels wide — 3.77 pixels per millimetre. A borrowed ring lines up with the circle at 17.3 mm inside diameter. That is 54.3 mm in circumference: US 7, UK N, EU 54. Checking a second ring gives 17.4 mm — still US 7 — so the buyer orders a 7.

Ring sizes around the world

The US and Canada use numbers from about 3 to 13 in quarter and half steps. The UK, Ireland, Australia and New Zealand use letters from A to Z, with half letters in between. Most of Europe and ISO standard sizing simply use the inside circumference in millimetres, so a 54 is 54 mm around. Japan and China use their own number scales, which start lower and step by about a third of a millimetre in diameter. Because the systems use different steps, conversions are close equivalents rather than exact matches.

When the on-screen method is not suitable

Rings with stones set low inside the band, very thin wire rings and rings that are not round are harder to measure on a screen. Some browsers also zoom pages; if the card never matches, reset the page zoom to 100% and calibrate again. If a ring is irregular, use a paper strip on the finger instead.

Privacy

Everything runs in your browser. Only your calibration setting is saved, locally in this browser; nothing is uploaded.