Use the free Ring Size Converter below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What the ring size converter does
Buying a ring online is hard when every shop seems to use a different size system. A ring that is a size 7 in the United States is not a size 7 anywhere else, and that single fact causes most wrong orders. This free ring size converter removes that confusion. You type in a size you already know, or a measurement from a ring that fits you, and it shows the matching size in the US, UK and EU systems, together with the inner diameter and the inner circumference in millimetres. Everything runs in your browser, so nothing you type is uploaded or stored anywhere.
The converter is built around a published size table. That table links each US size to a UK letter size and a European number, and it also gives the inside diameter and circumference for that size. When you type a diameter or a circumference instead of a size, the tool finds the nearest row in the table. That is the same approach a jeweller uses when they measure a ring on a mandrel, except here the work is done instantly and for free.
How to use it
Start with whichever piece of information you already have. If you know your US ring size, pick it from the list and press Convert. If you own a ring that fits well, measure the inside diameter across the middle of the ring with a ruler or calipers, and type that number in millimetres. If you measured around the inside of the ring with a strip of paper, type the circumference instead. The tool ignores the size list when you give a measurement, so the measurement always wins.
Read the big result at the top first. It gives all three sizes at once, so you can copy the one your shop asks for. Below it you will see the full table, which is useful when you are between sizes or when you want to check a second finger. Keep in mind that the table is a standard guide. Individual brands cut slightly larger or smaller, especially for wide bands, which tend to feel tighter than thin bands in the same size.
How to measure your finger correctly
Good measurement matters more than a good converter. Measure at the end of the day, when your fingers are at their largest, and measure the exact finger that will wear the ring, because fingers on your two hands are rarely the same size. Wrap a strip of paper snugly around the finger at the knuckle, mark where it overlaps, and measure the strip in millimetres. Do it twice, and if the two tries differ, take the larger one. Cold fingers shrink, warm fingers swell, and a ring that fits in winter can feel tight in summer, so avoid measuring straight after coming in from the cold.
If you are buying a surprise gift, the safest route is to borrow a ring the person already wears on that finger and measure its inside diameter. Do not guess from a ring worn on a different finger, because the difference between fingers is often a full size or more. If you are still unsure, many jewellers recommend sizing up rather than down, because a slightly loose ring can be adjusted more easily than one that will not go over the knuckle.
A worked example
Suppose your ring measures 17.3 millimetres across the inside. Type 17.3 into the diameter box and convert. The result is US 7, UK N and EU 54, with an inner circumference of 54.4 millimetres. If the shop you are buying from asks for a European size, you order 54. If it asks for a UK size, you order N. There is no extra maths to do and no second chart to look up, which is exactly the point of the tool.
Common questions
Why do US, UK and EU sizes look so different? They grew up separately. US sizes are numbers that rise in half steps, UK sizes are letters, and EU sizes are roughly the inner circumference in millimetres. They describe the same ring, just with different labels.
What if I am between two sizes? Pick the larger size, especially for a wide band or a ring you will wear in warm weather. A jeweller can usually make a loose ring slightly smaller, but a ring that is too small is harder to fix.
Does the same size fit every finger? No. Measure the exact finger. Your ring finger and your middle finger, and your left and right hands, will often differ by half a size or a full size.
Are these sizes exact? They follow the standard published table, but brands vary a little. Always check the brand size chart as well, and use this converter as the bridge between systems rather than as a replacement for the brand chart.
Limits of this tool
This converter translates between size systems. It cannot feel how a ring sits on your hand, and it cannot account for a very wide band, a swollen knuckle, or arthritis. If a ring is expensive or cannot be returned, get sized in a shop as well. For everyday orders, though, a careful measurement plus this conversion will get you the right size most of the time.