A ring that is too tight is uncomfortable, and one that is too loose can slip off and disappear. Getting the size right matters even more when the ring is a surprise, such as an engagement ring. Fortunately, you can measure your ring size at home with a few everyday items. This guide explains the most reliable methods, how to read a ring size chart, and the mistakes that lead to the wrong size.
How Ring Sizes Work
Ring sizes describe the inside of a ring. In the United States and Canada, sizes are numbers, usually from about 3 to 13, in quarter and half steps. The UK and Australia use letters, and much of Europe uses the inside circumference in millimetres. Whatever the system, everything comes back to two measurements: the inner circumference of the ring and its inner diameter.
Method 1: Measure a Ring You Already Own
If you have a ring that fits the right finger well, this is the most accurate home method.
- Place the ring on a flat surface.
- With a ruler marked in millimetres, measure the inside diameter from one inner edge straight across to the other, at the widest point.
- Compare the result with the chart below.
If you are buying a surprise engagement ring, borrowing a ring your partner wears on the ring finger of the correct hand is the classic trick. A ring worn on another finger will not give the right size.
Method 2: String or Paper Strip
- Cut a thin strip of paper or take a piece of non-stretchy string.
- Wrap it around the base of the finger, snug but not tight.
- Mark the point where the end overlaps with a fine pen.
- Check that the loop can slide over your knuckle; if it cannot, the size needs to be a little larger.
- Lay it flat and measure the length to the mark in millimetres. That is your finger circumference.
Paper is better than string, which can stretch or twist and give a reading that is too large. Measure two or three times to be sure you get the same result.
Method 3: A Ring Sizer
Plastic ring sizers, adjustable belts that look like small cable ties, and metal sizing sets are cheap and widely available, and many jewellers send them free. They are more accurate than string because, like a real ring, they are rigid and have width. If a lot is riding on the size, this is money well spent.
US Ring Size Chart
| US size | Inside diameter (mm) | Inside circumference (mm) |
|---|---|---|
| 4 | 14.9 | 46.8 |
| 5 | 15.7 | 49.3 |
| 6 | 16.5 | 51.9 |
| 7 | 17.3 | 54.4 |
| 8 | 18.1 | 57.0 |
| 9 | 19.0 | 59.5 |
| 10 | 19.8 | 62.1 |
| 11 | 20.6 | 64.6 |
| 12 | 21.4 | 67.2 |
Each full US size adds about 0.8 mm to the diameter and about 2.5 mm to the circumference. If your measurement falls between two sizes, choose the larger one, since a slightly loose ring is easier to adjust than one that will not fit over the knuckle. Charts from different jewellers can differ by a fraction of a millimetre, so check the brand’s own chart when you order.
Tips for an Accurate Measurement
- Measure at the end of the day. Fingers are usually slightly larger in the evening than in the morning.
- Avoid extremes of temperature. Cold shrinks fingers and heat swells them. Do not measure straight after exercise, a hot shower or coming in from the cold.
- Consider the knuckle. If your knuckle is much wider than the base of your finger, choose a size that slides over the knuckle and consider sizing beads or a slightly squared inner shape to stop it spinning.
- Measure the right finger on the right hand. Your dominant hand is often slightly larger.
- Think about band width. Wide bands, roughly 6 mm and over, feel tighter than thin ones, so many jewellers recommend going up about half a size.
- Measure more than once. Take readings on different days if you can.
Common Mistakes
- Using stretchy string or a flexible tape pulled too tight.
- Measuring the outside of a ring instead of the inside.
- Ignoring the knuckle.
- Guessing based on someone’s height or glove size, which does not translate reliably.
- Printing a paper sizer without checking the printer scale; set printing to 100% and check the reference ruler on the sheet.
Can a Ring Be Resized?
Most plain gold, silver and platinum bands can be resized up or down by one or two sizes. Some designs are much harder or impossible to resize, including eternity bands with stones all the way round, tension settings, and rings made of tungsten, titanium or ceramic. If you are unsure of the size for one of these styles, a sizer is essential. When you choose a wedding band to go with it, our guide on how to match a wedding ring to an engagement ring covers the fit between the two.
Buying a Ring as a Surprise
If you cannot measure directly, ask a close friend or family member who may know the size, or trace the inside of a ring your partner wears by pressing it into soft soap or drawing around it on paper, then measure the inside diameter of the tracing. When in doubt, choose a slightly larger size and a design that is easy to resize, and check the jeweller’s resizing policy before you buy.
Conclusion
For the most reliable result at home, measure a ring that already fits or use a proper ring sizer, measure at the end of the day, and choose the larger size if you fall between two. Then double-check against the jeweller’s own chart before you order.