Diamond Weight
Estimate diamond weight in carats, grams, and mg from dimensions, shape, and girdle thickness. Free tool for Round, Princess, Oval, Emerald, and 8 more shapes.
About This Calculator
The Diamond Weight Calculator estimates the weight of a diamond in carats, grams, and milligrams based on its dimensions, shape, and cut characteristics. Whether you are shopping for an engagement ring, evaluating a loose stone, or designing custom jewelry, this tool helps you quickly determine the approximate carat weight from simple measurements.
The calculation uses standard industry formulas developed by gemological institutes. For round diamonds, the formula is Diameter² × Depth × 0.0061 adjusted for girdle thickness. For fancy shapes (Princess, Oval, Emerald, Marquise, Pear, Heart, Cushion, Asscher, Radiant, Trillion, Baguette), the formula is Length × Width × Depth × Shape Factor × Girdle Factor × Correction Factor. The shape factor varies by cut and, for some shapes, by the length-to-width ratio. Girdle thickness adds 0% (thin) to 8% (extra thick) to account for additional material at the diamond's edge.
Diamond shapes differ in their weight-to-size ratios. Round brilliants are the most weight-efficient for their diameter, while fancy shapes like princess and cushion tend to be heavier for a given face-up area. The calculator supports 12 common shapes and includes both a shape-specific factor and an optional correction percentage for non-standard proportions, wide wings, or other variations.
Regional Notes: Carat weight is a universal standard (1 ct = 200 mg) used worldwide in India, the United States, the United Kingdom, and all major diamond markets. Diamond grading reports from GIA, IGI, and HRD all express weight in carats. Price per carat varies significantly by the 4Cs (Carat, Cut, Color, Clarity) and market conditions. In India, the Mumbai diamond bourse is a major trading hub. In the US and UK, diamond prices are typically quoted per carat in USD or GBP respectively.
Frequently Asked Questions
How is diamond weight calculated?
Diamond weight in carats is estimated using the formula: Length × Width × Depth × Shape Factor × Girdle Factor × Correction Factor. For round diamonds, the formula uses Diameter² × Depth × 0.0061 × Girdle Factor. Different diamond shapes have different shape factors ranging from 0.0057 for trillion to 0.00915 for baguette cuts.
How many carats is a 6.5 mm round diamond?
A 6.5 mm round diamond with average depth of 3.9 mm and medium girdle typically weighs approximately 1.00 carat. The exact weight depends on the depth percentage and girdle thickness of the specific stone.
What is the formula for diamond weight estimation?
For round diamonds: Weight = Diameter² × Depth × 0.0061 × Girdle Factor. For fancy shapes: Weight = Length × Width × Depth × Shape Factor × Girdle Factor × Correction Factor. Shape factors vary: Princess 0.0083, Oval 0.0062, Emerald varies by ratio, Pear varies by ratio. Girdle factors are Very Thin/Thin 1.00, Medium 1.02, Thick/Very Thick 1.05, Extra Thick 1.08.
What is a carat in diamond weight?
A carat is a unit of mass used for gemstones, standardized as 200 milligrams or 0.2 grams. One carat equals 200 mg. The term originated from carob tree seeds historically used as a reference for weighing gemstones.
How does girdle thickness affect diamond weight?
Girdle thickness directly affects diamond weight. A thicker girdle adds material and increases carat weight without increasing the visible face-up size. Very thin girdles add 0%, medium adds 2%, thick adds 5%, and extra thick adds 8% to the estimated weight. A well-proportioned diamond typically has a medium girdle.
Can I convert diamond carats to grams?
Yes, 1 carat equals 0.2 grams or 200 milligrams. To convert carats to grams, multiply the carat weight by 0.2. For example, a 1.5 carat diamond weighs 0.3 grams or 300 milligrams.
What are the different diamond shapes and their weight factors?
Common diamond shapes and their standard weight factors: Round 0.0061, Princess 0.0083, Oval 0.0062, Emerald 0.0080 (varies by ratio), Marquise 0.00565 (varies by ratio), Pear 0.00615 (varies by ratio), Heart 0.0059, Cushion 0.00815, Asscher 0.0080, Radiant 0.0081 (varies by ratio), Trillion 0.0057, Baguette 0.00915.
How accurate is diamond weight estimation from dimensions?
Diamond weight estimation from dimensions is typically accurate within 2-5% for well-proportioned stones. Factors like crown height, pavilion depth, culet size, and overall make can affect actual weight. For the most accurate measurement, a professional jeweler should weigh the diamond on a calibrated carat scale.