A complete San Marino ring-size guide for 2026 โ measure your finger or an existing ring, calculate the nearest Italian size, compare EU/ISO, US and UK equivalents, and use a printable millimetre reference before buying jewellery locally or online.
Use a narrow paper strip, mark the overlap, measure the length in millimetres and convert the result to an Italian ring size. A 54 mm circumference is approximately Italian size 14.
Use ordinary paper or a flexible non-stretch tape. Avoid elastic string.
Place it where the ring will sit and check that the loop can pass the knuckle.
Mark the exact overlap, lay the strip flat and measure from the starting edge.
Use the calculator and confirm the same millimetre measurement with the retailer.
Compare several readings taken under ordinary indoor conditions.
Use a jeweller for engagement rings, wedding bands and custom-made pieces.
| ๐ฎ๐น Italian Approx. | ๐ช๐บ EU / ISO | ๐บ๐ธ US | ๐ฌ๐ง UK Approx. | ๐ Inner Diameter (mm) | โญ Circumference (mm) | Diameter (cm) | Circumference (cm) | Reference |
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The chart rounds physical measurements to familiar retail labels. Keep the exact millimetre value when comparing different brands because conversion tables can differ by a quarter or half size.
Measure the finger on which the ring will be worn. The same finger on the opposite hand can have a different circumference, particularly on the dominant hand.
Cut a paper strip about 5โ8 mm wide or use a flexible non-elastic measuring tape. Thick cord, stretchy thread and soft string can distort the result.
The strip should touch the skin without compressing it. Check that the loop passes over the knuckle with gentle resistance and does not slide freely at the finger base.
Mark the exact overlap with a fine pen, lay the strip flat and measure from the starting edge to the mark. Enter the result as circumference in millimetres.
Take at least three readings during a normal part of the day. Avoid measuring immediately after sport, prolonged heat, a hot shower or exposure to cold weather.
Use a round ring that fits comfortably on the correct hand and finger. A ring from another finger is not a reliable substitute.
Place the ring flat and measure straight across the widest internal opening through the centre. Do not include either metal edge.
Turn the ring approximately 90 degrees and measure again. Different readings may indicate that the ring is slightly oval or distorted.
Select โExisting Ring Diameter in MM.โ A 17.3 mm internal diameter is near 54.4 mm circumference and approximately Italian size 14.
Example: 54 mm circumference โ 40 = Italian size 14.
Example: Italian size 14 + 40 = EU/ISO size 54.
17.3 mm diameter ร 3.1416 โ 54.4 mm circumference.
54.4 mm circumference รท 3.1416 โ 17.3 mm diameter.
5.44 cm circumference equals 54.4 mm circumference.
Use millimetres before matching an Italian or EU size chart.
First measure the calibration line with a physical ruler. It must be exactly 50 mm. Then place a comfortable existing ring over the circles and match the inside edge, not the outside edge.
Wedding bands and statement rings cover more skin than narrow rings.
The ring must pass the knuckle and remain secure at the finger base.
Heat can make fingers fuller, while cold can temporarily reduce the size.
Finger dimensions can differ between the left and right hands.
Elastic thread can tighten and produce a reading that is too small.
Rounded interiors can feel different from flat interiors at the same diameter.
These external references provide local jewellery context, technical sizing information and official consumer guidance: