Ring Size and Band Width Allowance

Ring sizing systems differ by country, and even within a single country there can be variation between jewelers. The most universally reliable measurement is the circumference of your finger in millimetres, because every sizing system can be derived from this single measurement.

How to measure your finger at home:

1. Cut a thin strip of paper about 3/4" (2 cm) wide and 4 inches (10 cm) long
2. Wrap it snugly (but not tightly) around the base of the finger you wish to size
3. Mark where the paper overlaps with a pen
4. Measure the distance from the end of the paper to your mark in millimeters
5. That measurement is your finger circumference

Best time to measure: late afternoon or evening, when fingers are slightly larger from normal swelling. Never measure when cold. Cold fingers shrink and give you a size that will not go on in July. For knuckle-heavy fingers (where the knuckle is much wider than the base), measure at the widest part.

Ring size conversion chart:

The Japan column is computed from the definition of the scale rather than copied from a chart, and it is worth saying because it did not used to be. Japanese size 1 is an inner diameter of 13.0 mm, and every size adds a third of a millimetre, so JP = (diameter − 13) × 3 + 1. The figures published around the internet drift from that by a size or two, which matters more at the top of the range than the bottom.

Diameter from circumference:

Diameter = Circumference / π (≈ Circumference / 3.1416)

System notes:

• US sizes use numbers with half sizes (5, 5.5, 6, 6.5…)
• UK sizes use letters (A–Z with half sizes like Z+1, Z+2)
• EU sizes are the finger circumference in millimeters, rounded to the nearest whole number
• Japanese sizes are inner diameter in millimetres, coded: size 1 is 13.0 mm, and each size adds a third of a millimetre

Band width and profile change the size you need, and this page accounts for both.

A wide band touches more of your finger, so it grips harder at the same nominal size. A narrow 2 mm band and a 8 mm band cut to identical inner diameters do not feel remotely alike, and the wider one will not pass the knuckle on a finger the narrow one fits.

Profile matters separately. A comfort fit band is domed on the inside, so only the centre of it touches your finger and it slides over the knuckle far more easily. Comfort-fit rings run about half a size larger in feel than a flat-interior standard fit, which means you order half a size down from your measured size. Get that backwards and the ring spins.

If you only want to convert a size you already know, the ring size converter does it live across US, UK, EU and Japan with no fit questions attached.

Online ordering tip: When buying a ring online without trying it on, order the most commonly suggested size for that finger and region. Average US women’s ring size: 6–7 (US) Average US men’s ring size: 10–11 (US) Those are averages only, and individual variation is wide enough that they are close to useless for one person.

Always consult a local jeweler for precise sizing before purchasing a non-resizable ring or an expensive piece.