Lab Grown Diamond Ring Size Chart
Finding the perfect ring size is just as important as choosing the perfect lab-grown diamond. Whether you're buying for yourself or planning a surprise proposal, this guide will help you measure accurately at home — with international conversion charts for Hong Kong, Mainland China, Japan, and US sizing.
At MadisonDia, every lab-grown diamond engagement ring is crafted to order, with D color, VVS clarity, and IGI or GIA certification. A correctly fitted ring sits comfortably at the base of your finger — neither sliding off nor leaving a deep mark. This guide shows you two simple ways to measure at home, plus a full international size conversion chart based on the Hong Kong jewelry standard.
📏 How to Measure Your Ring Size
You can measure your ring size at home using either an existing ring or a strip of paper. Both methods take less than two minutes.
Option 1 Measure an Existing Ring
This is the most accurate method if you already own a ring that fits the intended finger comfortably.
- Choose a ring that fits the intended finger well.
- Use a ruler to measure the inner diameter in millimeters (mm).
- Refer to the chart below to find the corresponding HK / CN size and your local equivalent.
Option 2 Use a Paper Strip
Don't have a reference ring? A simple strip of paper or string works just as well.
- Cut a thin strip of paper or string.
- Wrap it around the base of your finger (not too tight or too loose).
- Mark where the ends meet, then measure the length in millimeters (this is the circumference).
- Match the measurement with the chart below.
📐 International Ring Size Conversion Chart
MadisonDia uses the Hong Kong (HK) sizing standard — which is the same as the Mainland China (CN) retail standard used by major HK jewelers. Use this chart to convert your measurement into the correct HK / CN size, with Japan (JP) and US equivalents.
| Inside Diameter (mm) | Circumference (mm) | HK / CN | JP | US |
|---|---|---|---|---|
| 13.8 | 43.3 | 5 | 4 | 3 |
| 14.1 | 44.3 | 6 | 5 | 3¼ |
| 14.5 | 45.5 | 7 | 6 | 3¾ |
| 14.8 | 46.5 | 8 | 7 | 4 |
| 15.2 | 47.7 | 9 | 8 | 4½ |
| 15.5 | 48.7 | 10 | 9 | 5 |
| 15.9 | 49.9 | 11 | 10 | 5¼ |
| 16.2 | 50.9 | 12 | 11 | 5½ |
| 16.6 | 52.1 | 13 | 12 | 6 |
| 16.9 | 53.1 | 14 | 13 | 6¼ |
| 17.3 | 54.3 | 15 | 14 | 6¾ |
| 17.7 | 55.6 | 16 | 15 | 7¼ |
| 18.0 | 56.5 | 17 | 16 | 7½ |
| 18.3 | 57.5 | 18 | 17 | 8 |
| 18.7 | 58.7 | 19 | 18 | 8½ |
| 19.0 | 59.7 | 20 | 19 | 9 |
| 19.4 | 60.9 | 21 | 20 | 9¼ |
| 19.7 | 61.9 | 22 | 21 | 9¾ |
| 20.1 | 63.1 | 23 | 22 | 10¼ |
| 20.4 | 64.1 | 24 | 23 | 10½ |
| 20.8 | 65.3 | 25 | 24 | 11 |
| 21.1 | 66.3 | 26 | 25 | 11½ |
| 21.5 | 67.5 | 27 | 26 | 12 |
| 21.8 | 68.5 | 28 | 27 | 12¼ |
Chart based on the Hong Kong jewelry standard (used by Chow Sang Sang, Chow Tai Fook, and other major HK jewelers). HK and Mainland China retail sizing follow the same numerical system. If your measurement falls between two sizes, we recommend choosing the larger size for a more comfortable fit, especially for wider band designs.
💡 Ring Sizing Tips
Wider Bands Need More Room
Rings wider than 6mm typically need a half size larger for the same comfort level.
Temperature Matters
Cold fingers shrink. Warm them up first, or measure during the late afternoon when fingers are at their natural size.
Fit Test
A correctly sized ring slides on smoothly but requires a gentle pull over the knuckle to remove.
Surprise Proposal?
Borrow a ring she already wears on her ring finger and trace the inner circle on paper, then measure.
Measure Multiple Times
Take 3–4 measurements across different times of day and use the average for the most reliable result.
Resizing Available
MadisonDia offers complimentary first-time resizing within 30 days of delivery on most ring designs.
🎁 Buying a Ring as a Surprise Gift?
If you're planning a surprise proposal and can't measure her finger directly, try these discreet methods:
- Borrow a ring she already wears on the same finger and bring it to us — we'll measure it for you.
- Trace the inner circle of one of her rings on paper, then measure the diameter.
- Ask a close friend or family member who may know her size from past jewelry purchases.
- Choose a slightly larger size — it's much easier to resize a ring down than up, and we offer complimentary resizing.
📚 Continue Your Diamond Education
Now that you know your ring size, explore our other expert guides to make the perfect choice:
How to Choose the Best Engagement Ring
How to Choose a Lab-Grown Diamond
IGI vs GIA Certification Guide
MISI™ Diamond Sparkle Calculator
Engagement Ring Collection
Halo Diamond Rings
❓ Frequently Asked Questions
Is Hong Kong (HK) ring size the same as Mainland China (CN) size?
Yes — in retail practice at major Hong Kong jewelers (including MadisonDia, Chow Sang Sang, Chow Tai Fook), HK and CN ring sizes use the same numerical system. A HK size 14 is the same as a CN size 14 (≈16.9mm inner diameter). The chart on this page uses this unified HK/CN standard.
How accurate is measuring my ring size at home?
Home measurement is reliable when you follow the steps carefully and measure 2–3 times for consistency. For the most precise sizing, we recommend visiting a local jeweler to be sized with a professional ring sizer, or contacting our team for a complimentary plastic ring sizer to be mailed to you in Hong Kong.
What ring size does MadisonDia use by default?
MadisonDia uses Hong Kong (HK) sizing as the standard, which matches the Mainland China (CN) retail size system. The conversion chart on this page lets you convert from Japan (JP) or US sizes to find the correct HK/CN size for ordering.
Can I resize my MadisonDia ring later?
Yes. MadisonDia offers complimentary first-time resizing within 30 days of delivery on most ring designs (within 1–2 sizes up or down). Eternity bands and rings with channel-set diamonds along the entire band cannot be resized due to their construction. Contact our team for specific details about your design.
Should I order a slightly larger size to be safe?
If your measurement falls between two sizes, we recommend going up to the larger size. This is especially important for wider band designs (6mm or wider), as they sit more snugly than thin bands of the same nominal size. We can always resize down at no charge.
Do fingers really change size during the day?
Yes. Your fingers can swell by up to half a size in hot weather, after exercise, or in the evening, and shrink by a similar amount when cold or in the morning. The best time to measure is late afternoon at room temperature, which gives the most representative everyday size.
How do I measure my partner's ring size without them knowing?
The most reliable surprise-proposal method is to borrow a ring she already wears on her ring finger and either bring it to us for measurement or trace its inner circle on paper. If that's not possible, ask a close friend or family member who may have purchased jewelry for her in the past. As a last resort, choose a slightly larger size — we offer complimentary resizing.
Does MadisonDia ship a free ring sizer?
For customers in Hong Kong and surrounding regions, we can mail a complimentary plastic ring sizer on request. Please contact our team with your shipping address to arrange this.
Still Unsure About Your Ring Size?
Our diamond consultants are here to help — from sizing questions to custom design previews.
Contact Us Design Your Ring