Ring size calculator
Enter your finger measurement, choose units and preferred fit. The calculator estimates circumference, selects the closest standard size, and shows neighbouring options for comparison.
Tips for accurate ring sizing
- Measure at the end of the day, not in the morning.
- Measure several times and use the average for better accuracy.
- A ring should slide over the knuckle with slight resistance.
- Consider wider bands slightly larger than thin bands.
This calculator uses approximate formulas and standard charts. For very valuable jewellery, confirm the final size with a professional jeweller.
Example ring size data table
The following table shows example finger circumferences and approximate international ring sizes. Values are rounded and may vary slightly between manufacturers.
| Finger circumference (mm) | Approx. US size | Approx. UK size | Approx. EU/ISO size | Approx. diameter (mm) |
|---|---|---|---|---|
| 44.2 | 3.0 | F | 44.2 | 14.1 |
| 49.5 | 5.0 | J | 49.5 | 15.8 |
| 54.5 | 7.0 | N | 54.5 | 17.3 |
| 57.0 | 8.0 | P | 57.0 | 18.1 |
| 62.1 | 10.0 | T | 62.1 | 19.8 |
Formula used
This ring size calculator combines your measurement with approximate conversion formulas and a generated standard size table to estimate common international ring sizes.
- Circumference from diameter: circumference(mm) = diameter(mm) × π.
- Linear approximation for US sizes: circumference(mm) ≈ 36.475 + 2.575 × US_size.
- Diameter from circumference: diameter(mm) = circumference(mm) ÷ π.
- EU/ISO size approximation: EU_size ≈ circumference(mm) rounded to one decimal place.
- Comfort adjustment: If knuckle is provided, comfort circumference = average of finger and knuckle measurements, then slightly adjusted for fit preference.
These formulas are approximations. Individual brands and regional standards may use slightly different charts, so always confirm final sizing before purchasing custom jewellery.
How to use this calculator
- Wrap a flexible measuring tape or strip of paper around the base of the finger where the ring will sit. Mark the overlap.
- Measure the length between marks. Enter it as circumference, choosing millimetres or inches from the unit selector.
- If measuring diameter instead, place a ring that already fits on a ruler. Measure the internal diameter and choose diameter.
- Optionally, measure around the knuckle using the same unit and enter the value in the knuckle circumference field.
- Select your preferred fit: snug, comfort, or slightly loose. Comfort fit usually works well for most ring styles.
- Click “Calculate ring size”. Review the recommended size along with one size smaller and one size larger for comparison.
- Use the CSV button to download the comparison table and the PDF button to generate a printable report for record keeping.
Ring size and daily comfort
Your ring size affects how a band feels during everyday tasks such as typing, washing dishes or carrying bags. A correctly chosen size should not pinch, leave deep marks or spin constantly, but remain secure and comfortable throughout normal movement.
Coordinating ring size with other accessories
Jewellery often complements your wardrobe. A snug but comfortable ring pairs well with properly fitted clothing and footwear. Use a clothing size calculator and a shoe size calculator to keep outfits balanced while this tool ensures your rings feel as good as they look.
International ring size conversions in practice
Travelling or ordering from overseas retailers means navigating different size systems. This calculator converts your measurement into approximate US, UK and EU sizes so you can match product listings, avoid guesswork and reduce the chance of costly returns or resizing after delivery.
Ring size for different band widths
Wide bands cover more skin and can feel tighter than slim bands with the same labelled size. When shopping for chunky designs, consider selecting a slightly larger size than your everyday thin stacker, especially if your knuckles are prominent or fingers swell in warm weather.
Planning surprise gifts using ring size
When buying a surprise engagement, promise or anniversary ring, accurate sizing becomes trickier. Discreetly borrow an existing ring from the same finger, trace its inner circle, then compare with this calculator’s chart to estimate a size that keeps alterations minimal after the proposal or celebration.
Tracking ring size changes over time
Finger size can change after weight fluctuations, pregnancy or lifestyle adjustments. Saving your calculated results lets you compare measurements taken months or years apart, decide whether existing rings need resizing, and plan future jewellery purchases with more confidence in long term comfort and fit.
Frequently asked questions
How accurate is this ring size calculator?
This tool uses your measurements with standardised charts to estimate ring sizes across several systems. It is usually accurate for everyday use, but manufacturing tolerances, band width and finger shape mean professional confirmation is recommended for expensive or bespoke jewellery.
What happens if I measure too tight or too loose?
Measuring loose gives a ring that may spin or slip off, especially in cooler temperatures. Measuring too tight can make the ring difficult to remove. Aim for a gentle pull over the knuckle and comfortable, even contact around the finger all day.
Do wide bands require a different ring size?
Wider bands cover more of your finger, so they often feel tighter than thin bands in the same nominal size. For very wide or chunky rings, many jewellers recommend choosing approximately half a size larger than your everyday narrow band size.
Can I measure my ring size accurately at home?
You can measure at home using a flexible tape, printable ring sizer strip or an existing ring that fits well. For the most reliable result, combine home measurements with an in store sizing session at a jewellery counter.
Why does my ring size change during the day?
Finger size changes with temperature, hydration, activity and even time of day. Warm conditions and exercise make fingers slightly larger. Cold weather and dehydration can shrink them. That is why measurements taken at several times are more trustworthy.
How should I use the results when ordering jewellery?
Use the calculator to narrow down a comfortable size range, then test neighbouring sizes whenever possible. For a surprise gift, borrow a ring from the same finger, trace its inner circle, and double check against our chart before ordering.