Ring Sizes Explained: UK Chart, mm Conversions and Band Width

The table covers I to Z+1, the range most adult hands fall into (our sizes go up to Z+7 / US 16). The mm columns are the standard UK measurements for each letter. The US sizes are the ones each letter is paired with in our size menu, chosen from experience fitting our comfort-fit bands, so they differ slightly from general conversion charts. Half sizes, and French, German, Japanese and Swiss sizes, are on our ring size chart page, whose US column follows the general standard; for ordering, use the pairs above.

EU (ISO) sizes are simply the inside circumference in mm, so an EU 58 reads straight off the chart: it falls between Q / US 8 and R / US 8.5, about 18.5mm across. Some charts round 58 up to R, so if you're between the two, a metal sizer settles it.

If you already know your US size, choose it in the size menu: each UK letter is paired with a US size, half a size apart, from I / US 4 to Z+7 / US 16. A 17mm inside diameter lands between M and N on the chart, so N / US 6.5 is the size to confirm with a sizer.

Treat every conversion as approximate. Neighbouring letters are only about 0.4mm apart in diameter and charts round differently, so if a reading falls between rows, confirm with a metal sizer in the width of your band and take the larger size.

Ring Sizer Tool - US Sizes 2 - 13 | Accurate Ring Sizing Guide

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The detachable sizer tool covers US sizes 2 to 13 and gives you a US number to convert here. Pick the piece that sits snug but comfortable, shake your hand to check it stays put, and wear it for a few hours of normal activity. Check the size menu on the product page before you decide.

A 17mm figure is almost certainly an inside diameter. Adult finger diameters run roughly 14mm to 23mm and circumferences about 44mm to 72mm, so anything in the teens or low twenties is a diameter and anything from the mid-forties upwards is a circumference.

That settles the common ones: a 2cm (20mm) ring is about U / US 10. A '6cm finger' is a 60mm circumference, which is roughly 19.1mm across, so S / US 9. A reading of 88.9mm fits no finger at all; it is exactly 3½ inches, so you've probably read the inch scale, or wrapped round the knuckle with slack. Measure again.

To measure a ring that already fits, use calipers or a clear mm ruler and read from inner edge to inner edge straight through the centre. On a comfort-fit band, measure at the middle of the interior, where the opening is smallest, then rotate the ring 90 degrees and average the two readings. If you only have a circumference, divide by 3.14 for the diameter.

This method only holds if that ring goes on the same finger, is a similar width and fits well today. A 2mm and an 8mm band with identical diameters will not feel the same on your hand.

6mm Metal Ring Sizer

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For a mid-width band, the 6mm sizer confirms the number properly: solid stainless steel with the same comfort-fit interior as the finished bands, so the fit you try is the fit you get.

The most reliable way to find your UK ring size at home is a solid metal sizer in the same width as the band you want; string and paper are rough guides only. In order of trust:

1. Same-width steel sizer: best, because it tests the knuckle and allows for width.
2. The US 2–13 sizer tool: good, but allow for width (next section).
3. A ring that already fits: good if the width is similar and it goes on the same finger.
4. String or paper strip and a ruler: a starting point, not an answer.

For the string method, wrap it snugly round the base of the finger, mark where the ends meet, measure in mm and read that circumference against the chart or the ring size finder. It can be a size or more out because string digs into soft tissue and reads small, paper overlaps unevenly, and neither tells you whether a rigid band will pass over your knuckle (see metal versus plastic sizers).

Fingers change through the day, often by half a size or more. Measure late afternoon or evening at room temperature, not after exercise, a hot shower, time out in the cold, alcohol or salty food, and not first thing in the morning when fingers are puffy. Measure the exact finger on the exact hand, since the dominant hand is often slightly larger, and repeat on two or three different days.

4mm Metal Ring Sizer

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The metal sizers are available in 4mm, 6mm and 8mm widths from the ring sizers collection. Order your estimated size plus one either side, compare them, then wear the winner for 15 to 20 minutes while moving your hand, because a size that felt fine at first can tighten as the finger warms.

Yes: a wider band touches more skin, so a 6mm or 8mm ring in the same letter feels tighter than a 4mm one. Most of our bands are 4mm, 6mm or 8mm wide, which is why the sizer you use should match the width you are buying.

The allowance in the last column only applies if you measured with something narrower, such as the thin sizer tool, string or a slim ring. A same-width metal sizer already accounts for width, and adding more would leave the ring loose. For a 7mm band the 8mm sizer is the closest match, and the finished ring will feel very slightly roomier.

Our metal bands have a comfort-fit profile: a gently rounded interior (see comfort fit and standard fit) that slides over the knuckle more easily than a flat-interior band and can feel a touch less snug, so you may need less allowance than the table suggests. All our comfort fit rings use this profile; the metal sizers share it, so a sizer that fits is the fit you'll get.

Material matters too. Tungsten, tungsten carbide and black zirconium are very hard and generally cannot be resized, so measure carefully. With wood or bone inlays, size up slightly if you have prominent knuckles.

8mm Metal Ring Sizer

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Matching sets are labelled Ring 1 / Ring 2 and come in fixed width pairings such as 4mm & 6mm, with each ring sized separately. Each partner measures their own finger with the sizer that matches their own band width, one with the 4mm sizer and the other with the 6mm, since the two widths fit differently in the same letter. Our guide to matching wedding ring sets covers choosing the pairing.

Every ring arrives with a complimentary silicone ring and a ring box. Wear the silicone ring day to day at your chosen size to check comfort through work, training and warm afternoons, bearing in mind that silicone flexes as a finger swells while a metal band stays the same size, so the metal sizer remains the final word.

Braided Stackable Silicone Ring Bay Blue 3mm Width

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Interior engraving is available, so confirm your UK letter (see free ring sizer) before adding it.

If the size is still wrong, the 90-day size exchange applies, with details in our Refunds and Returns policy. UK returns use a prepaid Royal Mail Tracked Returns 48 label to our Wokingham PO Box; Australian and New Zealand returns go to our PO Box in Christchurch. Everything also carries a one-year warranty from the day the order arrives, covering defects in materials and workmanship.