The complete 2026 Australian-to-American ring size guide โ convert AU letter sizes to US numbers, calculate from finger circumference or inner diameter, compare millimetres and inches, and check fit before ordering from an Australian or US jeweller.
AU to US Ring Size Conversion provides a practical letter-to-number estimate and then verifies that estimate with physical measurements. Select an Australian letter in the converter, or enter a circumference or inner diameter. The result displays the nearest US half size, the approximate AU size, EU/ISO circumference and exact millimetre values.
The conversion is intentionally described as approximate because retail charts do not always round letters and half sizes in exactly the same way. Michael Hill Australia confirms that Australia uses a letter system and recommends measuring the internal diameter in millimetres or measuring finger circumference. The Tiffany Australia ring guide also pairs Australian letters with US numbers and inner diameters.
These are practical nearest-size references for frequently purchased ring sizes. Half-letter availability varies, so use the complete chart and millimetre columns for a more careful comparison.
Australian listings commonly use letters similar to the UK convention.
US listings commonly use 5, 5.5, 6, 6.5 and similar numeric steps.
A 17.3 mm diameter is about 54.4 mm circumference.
A 57 mm circumference is about 18.1 mm diameter.
Convert American inch measurements before comparing a metric chart.
Use the letter and number as labels; use millimetres as the final check.
| ๐ฆ๐บ AU Size | ๐บ๐ธ US Size | ๐ Inner Diameter | โญ Circumference | ๐ช๐บ EU / ISO | ๐ Diameter (in) | Reference |
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Choose a round ring worn comfortably on the exact finger and hand intended for the new ring. A ring from the opposite hand or another finger may have a different internal size.
Place the ring on a millimetre ruler and measure straight across the widest inner opening through the centre. Do not include either metal edge. Record one decimal place, such as 17.3 mm.
Turn the ring approximately 90 degrees and measure again. Matching readings indicate a round ring. If the readings differ, the ring may be oval and should be checked professionally.
Select Existing Ring Inner Diameter in MM. The converter identifies the nearest US number and AU letter while retaining the exact physical measurement for comparison with the seller's chart.
Cut a strip around 8โ10 centimetres long. Paper is generally easier to control than elastic string, which can stretch and underestimate the required size.
Wrap the strip around the base of the finger so it touches the skin without compressing it. Check that the loop can pass over the knuckle with gentle resistance.
Use a fine pen to mark the overlap. Lay the strip flat and read the distance from its starting edge to the mark in millimetres. A reading of about 54 mm is close to AU N and US 7.
Measure at least three times when the hand is comfortably warmโnot immediately after exercise, cold exposure or a hot shower. Use the consistent result rather than a single extreme reading.
Disable โfit to pageโ, โshrinkโ and other scaling. First confirm that the line below measures exactly 50 mm. Place a comfortable ring over a circle and align the ring's inside edgeโnot its outside edgeโwith the circle.
Ring labels are category names rather than perfectly universal physical measurements. One Australian chart may place a diameter at N, while another may use Nยฝ. A US seller may manufacture quarter sizes, half sizes or only whole numbers. The nearest available product can therefore differ from the mathematically closest result.
Use the converter for a starting point, then compare the exact diameter and circumference against the product's own chart. When contacting support, include the ring style and band width because a broad comfort-fit band can feel different from a narrow flat-profile ring.
ISO 8653:2016 specifies professional methods for measuring and designating ring sizes using defined tools. Consumer home measurement is useful for estimating, but a jeweller's ring stick and finger gauges provide a controlled final check.
For valuable, full-eternity, engraved, tungsten or difficult-to-resize rings, ask the retailer to confirm which exact internal measurement corresponds to the displayed AU or US label before payment.
More metal contacts the finger, so additional room may be recommended.
The ring must clear the knuckle while staying secure at the finger base.
Heat can enlarge fingers temporarily; cold can make them smaller.
Several rings worn together can feel tighter than one ring alone.
Tungsten and some titanium designs may require exchange rather than resizing.
Rounded interiors can feel different from flat interiors at the same diameter.
A retailer lists a ring as AU N. A matching measurement near 17.2โ17.3 mm inner diameter or about 54 mm circumference is commonly close to US 7. The product's own chart should decide whether N or Nยฝ is the nearest label.
An 18.1 mm inner diameter corresponds to about 57 mm circumference. Pandora's published international chart places this measurement at US 8 and UK/AU P. A different Australian retailer may use P or a nearby half-letter.
US 9 is approximately 18.9 mm diameter and 59.5โ60 mm circumference. Australian charts often place this area around Rยฝ to S. Send the millimetre measurement to the store rather than relying on the letter alone.