MmToCaratConversion
Convert diamond mm dimensions to carat weight for round brilliant princess emerald cushion oval heart marquise pear radiant asscher trillion and baguette shapes with girdle correction.
About This Calculator
The MM to Carat Conversion Calculator helps jewelers, gemologists, and diamond buyers estimate the weight of a diamond from its millimeter dimensions. Unlike simple multiplication calculators, this tool uses the standard GIA diamond weight formula with shape-specific correction factors and girdle thickness adjustment for accurate results across 12 popular diamond cuts.
For round brilliant diamonds, the formula is: Diameter² × Depth × 0.0061 × Girdle Factor. For fancy shapes (princess, emerald, cushion, oval, heart, marquise, pear, radiant, asscher, trillion, baguette), the formula is: Length × Width × Depth × Shape Factor × Girdle Factor. Each shape has a unique coefficient ranging from 0.0057 for trillion cuts to 0.0090 for baguette cuts, reflecting how the shape's geometry affects weight per millimeter.
Girdle thickness correction accounts for the diamond's outermost edge — very thin girdles use a 0.98 multiplier while very thick girdles use 1.06. A diamond with a thicker girdle weighs more for the same face-up size, so accurate girdle assessment is important for precise weight estimation.
Regional Notes
India: Diamond weight is measured in carats globally. Indian jewelers typically use the same GIA standards. The ISB (Indian Standard Bureau) recognizes 1 carat = 200 mg. Common diamond sizes in Indian jewelry range from 0.10 ct (3 mm round) to 2 ct (8 mm round).
US: The Federal Trade Commission regulates diamond weight disclosure. US jewelers use the same GIA formula. Popular engagement ring center stones range from 0.5 ct (5 mm round) to 1.5 ct (7.3 mm round). Always get a certified grading report for stones over 0.5 ct.
UK: The National Association of Goldsmiths (NAG) follows the same standards. UK buyers often use points (100 points = 1 carat) in addition to carat decimals. The formula and correction factors are universal across all markets.
Uses of this Calculator
This tool helps verify if a diamond's reported weight matches its physical dimensions, estimate weight when only dimensions are known (e.g., loose diamonds in settings), compare face-up size across different shapes for a target carat weight, and educate buyers on how shape and cut affect diamond weight.
Frequently Asked Questions
How do you convert diamond mm to carat weight?
For round brilliant diamonds the formula is Diameter squared times Depth times 0.0061 times girdle correction factor. For fancy shapes the formula is Length times Width times Depth times the shape-specific factor times girdle correction factor. Each shape has a unique factor: round 0.0061 princess 0.0082 emerald 0.0080 cushion 0.0065 oval 0.0062 heart 0.0060 marquise 0.0067 pear 0.0062 radiant 0.0082 asscher 0.0080 trillion 0.0057 baguette 0.0090.
What is the formula for diamond weight calculation?
The standard GIA formula for diamond weight is: for round diamonds — Diameter squared times Depth times 0.0061; for fancy shapes — Length times Width times Depth times shape factor. The result is then multiplied by a girdle thickness correction factor ranging from 0.98 for very thin to 1.06 for very thick girdles.
How many carats is a 6 mm round diamond?
A 6 mm round brilliant diamond with 2 mm depth weighs approximately 0.44 carats using the formula 6 squared times 2 times 0.0061. Actual weight varies with depth percentage and girdle thickness. A well-cut 6 mm round diamond typically weighs between 0.40 and 0.50 carats.
What is girdle thickness in diamond weight calculation?
Girdle thickness refers to the outermost edge of a diamond expressed as a percentage of diameter. Very thin girdles use a 0.98 correction factor medium girdles use 1.00 and very thick girdles use up to 1.06. Thicker girdles add weight without increasing visible face-up size so they should be accounted for in accurate weight estimation.
What is a shape correction factor for diamonds?
The shape correction factor adjusts the diamond weight formula for non-round fancy shapes. Each shape has a specific factor: round 0.0061 princess 0.0082 cushion 0.0065 oval 0.0062 heart 0.0060 marquise 0.0067 pear 0.0062 emerald 0.0080 radiant 0.0082 asscher 0.0080 trillion 0.0057 and baguette 0.0090.
Is the MM to Carat Conversion Calculator free to use?
Yes the MM to Carat Conversion Calculator is completely free to use with no registration required. You can calculate diamond weight for any shape adjust girdle thickness and share results via URL.
Can I share my diamond weight calculation results?
Yes the calculator saves your inputs in the URL so you can share the exact diamond dimensions shape and girdle settings with jewelers or friends by copying the page URL.
Do different diamond cuts affect carat weight calculation?
Yes different cuts have different shape factors in the formula. Princess and radiant cuts use 0.0082 which gives higher weight per mm compared to round at 0.0061. Heart and trillion shapes use lower factors because their shape removes more material. Always select the correct shape for accurate weight estimation.