💍Ring Size Calculator
Find your ring size from inside diameter or circumference, or convert between US, UK/Australia, France/Russia, Germany, Switzerland, and Japan ring sizes.
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Inside Circumference (mm)
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Ring Size Calculator
Ring sizing is not universal — different countries use entirely different scales. A US size 7, a UK size N, a French size 54, and a German size 18 all refer to the same physical ring. This calculator converts between all major international sizing systems or finds your size from an inside diameter or circumference measurement.
Quick measure: measure the inside diameter of an existing ring in mm, or wrap a strip of paper around your finger to get the inner circumference in mm.
Buying a ring — whether as a gift, for an engagement, or as a fashion item — from an international retailer requires knowing the correct size in the vendor's local system. Getting the size wrong means an expensive return or resizing fee. This guide explains how each sizing system works, how to measure accurately at home, and what to do when a size falls between standards.
How to Measure Your Ring Size at Home
There are two reliable home measurement methods:
- Diameter method (existing ring): Lay the ring on a flat surface and measure the inside diameter — the distance from one inner edge to the opposite inner edge — in millimetres using a ruler or digital calipers. This is the most accurate home method.
- Circumference method (finger): Wrap a thin strip of paper or a piece of string around the base of the target finger. Mark where the strip overlaps, then lay it flat and measure the length in millimetres. This is your inside circumference. Divide by π (3.14159) to get the equivalent diameter.
Enter either measurement above and the calculator will identify the closest standard size across all supported systems simultaneously.
International Ring Sizing Systems Explained
| System | Countries | Based On | Example (≈17 mm dia.) |
|---|---|---|---|
| US / Canada | United States, Canada | Arbitrary numeric scale | Size 7 |
| UK / Australia | UK, Australia, Ireland, NZ | Letter scale (A–Z+) | N |
| France / Russia | France, Russia, SE Asia | Inner circumference (mm) | 54 |
| Germany | Germany, Netherlands | Inner diameter (mm) | 17 |
| Japan | Japan | Numeric scale (~0.8 mm/step) | 13 |
Tips for Accurate Sizing
- Time of day matters: Fingers swell slightly in warm weather, after exercise, or later in the day. Measure in the afternoon for the most representative size, not first thing in the morning when fingers are at their smallest.
- Knuckle vs base sizing: If your knuckle is significantly larger than the base of your finger, size to fit over the knuckle and use a clear ring guard or sizing adjuster to prevent the ring from spinning once past the knuckle.
- Band width adjustment: Wider bands (above 6 mm) fit more snugly against the finger than narrow bands of the same inside diameter. If you are ordering a wide band such as a wedding ring, consider sizing up half a size from your measured size.
- Between sizes: Not every increment in every system has a direct equivalent in other systems. When sizes fall between standards, choose the larger size for rings you will wear daily — comfort improves with a slightly looser fit.
Ring Resizing: What You Should Know
Most plain metal rings — gold, silver, platinum — can be resized by a jeweller within a range of about two sizes up or down. The process involves either stretching/compressing the shank or cutting the band and adding/removing material. Rings with channel-set stones around the entire band (eternity rings) typically cannot be resized without disturbing the stones. Titanium and tungsten carbide rings cannot be resized at all due to the hardness of the material — when ordering these, getting the size right before purchase is critical.
How Ring Sizes Differ by Finger
The dominant hand's fingers are typically slightly larger than the non-dominant hand's fingers on the same person — usually by half a size. Ring sizes also vary significantly across fingers: the pinky is typically size 4–5 (US), the ring finger 6–7, the middle finger 7–8, and the index finger 7–9. Size both the specific finger and hand before ordering a ring that cannot easily be returned or resized.
Frequently Asked Questions
How do I measure my ring size at home without a ring sizer?
Wrap a thin strip of paper or a piece of string snugly around the base of the finger you plan to wear the ring on. Mark where the strip overlaps and measure that length in millimetres — this is your inner circumference. Divide by 3.14159 to get your inner diameter. Alternatively, measure the inside diameter of a ring that already fits well using a ruler or digital calipers. Enter either value into this calculator to find your size in all international systems.
What is the most common ring size for women and men?
For women, the most common ring finger size in the US is size 6 (approximately 16.5 mm diameter). For men, the most common size is 9 (approximately 19 mm diameter). These are averages — finger size varies considerably by height, weight, age, and ethnicity. Always measure the specific finger before ordering rather than relying on average size charts.
Why does the size of my ring feel different in winter versus summer?
Fingers change size with temperature and hydration. In cold weather, blood vessels constrict and fingers shrink slightly, making rings feel looser. In warm weather or after drinking a lot of water, fingers swell slightly, making the same ring feel tighter. This variation can be as much as a full size across the year for some people. Measure your ring size during temperate conditions for the most representative everyday fit.
Can I convert a US ring size to UK size directly?
US and UK ring sizes are based on different measurement systems — the US uses an arbitrary numeric scale and the UK uses an alphabetical scale based on circumference increments. The conversion is not a simple formula but a lookup from a reference table. In this calculator, entering any known size in one system instantly shows the equivalent in all other systems. For example, US size 7 corresponds to UK size N, French size 54, and German size 17.
How much does it cost to resize a ring and can all rings be resized?
Resizing a plain gold or silver band typically costs $20–$100 depending on the metal and the amount of resizing needed. Platinum costs more to resize due to the material's density. Eternity rings with stones set all the way around cannot be resized without disturbing the stones. Titanium and tungsten rings cannot be resized at all because of their hardness. Always confirm resizability with a jeweller before purchasing if you are unsure of the size.
Should I size up or down if I am between ring sizes?
For everyday wear, sizing up is generally more comfortable — a slightly loose ring is easier to put on and take off, and swelling throughout the day will not make it uncomfortable. For rings on fingers with a pronounced knuckle (where the knuckle is much wider than the base), size to fit over the knuckle and use a ring guard to keep it snug at the base. For narrow stacking rings, sizing down is often preferred for a secure fit.
Does ring width affect what size I should order?
Yes. A wider band sits against more finger surface, which means it fits more snugly than a narrow band of the same diameter. The general guideline is to size up by half a US size for bands between 6–8 mm wide, and a full size for bands over 8 mm wide. This adjustment is most important for wedding bands and wide fashion rings. Narrow bands (under 4 mm) typically do not require an adjustment from your measured size.