A ring size calculator helps you find the perfect fit when buying rings online or converting between international sizing systems. Ring sizes vary widely across countries — the US uses a numeric scale, the UK uses letters, and Europe uses millimeters. Whether you already know your size in one system or need to measure your finger from scratch, this free tool converts between all major standards instantly.
Convert Between Ring Sizes
Enter a size in any field to convert to all other systems instantly.
How to Measure Your Ring Size at Home
String method: Cut a thin strip of paper or string. Wrap it snugly around the base of the finger you want the ring on. Mark where it overlaps, then measure the strip's length in millimeters. That is your circumference.
Existing ring method: Place a ring that fits well on a ruler. Measure the inside distance across (diameter) in millimeters.
Tips: Measure at the end of the day when fingers are slightly larger. Measure 3-4 times for accuracy. Consider going up half a size for wide band rings (over 6 mm).
Complete Ring Size Chart
| US | UK | EU | Diameter (mm) | Circumference (mm) |
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How to Use the Ring Size Calculator
Finding the right ring size is critical when shopping for engagement rings, wedding bands, or any ring purchased online. An ill-fitting ring can slip off and get lost, or feel uncomfortably tight throughout the day. This free ring size calculator takes the uncertainty out of the process by converting between all major international sizing systems and helping you determine your size from a simple finger measurement.
Step 1: Choose Your Mode
Select "I Know My Size" if you already have a ring size in one system and want to convert it to another. For example, if you know your US size and need to order from a European jeweler, this mode gives you the EU equivalent instantly. Select "Measure My Finger" if you are starting from scratch and need to determine your size from a physical measurement.
Step 2: Convert Between Systems
In Convert mode, select or type a size in any field — US, UK, EU, inner diameter (mm), or inner circumference (mm). All other fields update automatically. The US system uses numeric sizes from 0 to 16 with half-size increments. The UK system uses letters from A to Z, including half letters. European sizes correspond to the ring's inner circumference in millimeters rounded to the nearest whole or half number.
Step 3: Measure and Find Your Size
In Measure mode, you have two options. The string method involves wrapping a strip of paper or string around your finger, marking where it overlaps, and measuring its length. Enter that circumference in millimeters. The existing ring method works by measuring the inner diameter of a ring that already fits well. Place it on a ruler and measure the distance across the inside in millimeters. Both methods show your closest size in US, UK, EU, and metric formats.
Step 4: Use the Size Chart
Scroll down to the complete ring size chart for a side-by-side comparison of all sizes. Common sizes are highlighted — US 6-7 for women and US 9-10 for men. The chart includes inner diameter and circumference measurements so you can cross-reference with any measurement method.
Tips for the Most Accurate Fit
Fingers change size throughout the day due to temperature, hydration, and activity level. For the most reliable reading, measure at the end of the day when fingers tend to be slightly larger. Take 3-4 measurements over different days and use the average. If the ring has a wide band (over 6 mm), consider going up half a size since wide bands fit more snugly. If you are between two sizes, the larger size is usually the safer choice for comfort.
FAQ
Is this ring size calculator really free?
Yes, this ring size calculator is completely free with no limits, no ads-walls, and no signup required. Every conversion runs instantly in your browser, and you can use it as many times as you need.
Is my data safe when using this tool?
Absolutely. Everything runs locally in your browser — no data is sent to any server. Your measurements are never stored, tracked, or shared with anyone.
How do I measure my ring size at home?
Wrap a thin strip of paper or string snugly around the base of your finger. Mark where it overlaps, then measure the length in millimeters. Enter that circumference into the Measure mode of this tool to find your closest ring size in all international systems.
What is the most common ring size for women?
The most common women's ring sizes are US 6 and US 7, which correspond to UK L-N, EU 51.5-55, and an inner circumference of roughly 52-55 mm. However, ring size varies by finger and individual, so measuring is always recommended.
What is the most common ring size for men?
The most common men's ring sizes fall between US 9 and US 10, which correspond to UK R.5-T.5, EU 59-63, and an inner circumference of about 60-63 mm. For an accurate fit, always measure the specific finger you plan to wear the ring on.
Should I size up or size down for a wide band ring?
Wide band rings (over 6 mm) tend to fit tighter than narrow bands. Most jewelers recommend going up half a size for bands wider than 6 mm. This calculator shows you surrounding sizes so you can easily compare.
Do ring sizes differ between countries?
Yes, each country uses a different ring sizing system. The US uses a numeric scale (0-16 with half sizes), the UK uses an alphabetical scale (A-Z), and most European countries use inner circumference in millimeters. This tool converts between all major systems instantly.
When is the best time to measure my finger for a ring?
Measure at the end of the day when your fingers are at their largest. Avoid measuring when your hands are cold, wet, or right after exercise. For best accuracy, measure 3-4 times on different days and use the average.