Side-by-Side Comparison
Jewelry & Precious Metals
Diamond Carat to Millimeter Sizes vs. Gold Karats & Fineness Hallmarks
Comparing 2 standards across 16 specifications. 16 key differences identified.
Comparing:
Diamond Carat to Millimeter Sizes
Gold Karats & Fineness Hallmarks
Diamond carat weight is standardized under the Gemological Institute of America (GIA) where 1.00 metric carat equals exactly 0.200 grams (200 milligrams / 100 points). For an ideal 'Triple Excellent' round brilliant cut, carat weight translates into exact face-up millimeter diameters, from 0.10 ct (3.0 mm) to 3.00 ct (9.4 mm).
Precious metal fineness is standardized under ISO 9202 and national hallmark regulations in parts per thousand (millesimal fineness) and traditional karats (24ths of pure gold), defining the exact alloy ratios of pure 24K (999), 18K (750), 14K (585), 10K (417), Sterling Silver (925), and Platinum (950).
Specification Comparison Table
16 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
GIA / ISO 24016 (Jewellery — Diamond grading) / CIBJO Diamond Book | ISO 9202 / ISO 11426 (Fire Assay) / FTC 16 CFR Part 23 / UK Hallmarking Act |
|
Carat Weight Definition
|
1.00 Carat (1.00 ct) = Exactly 0.200 grams (200 mg / 100 Points) | — |
|
0.25 Carat (1/4 ct / 25 Pts)
|
Diameter: 4.1 mm ± 0.1 mm | Surface Area: ~13.2 mm² | Subtle accent solitaire | — |
|
0.50 Carat (1/2 ct / 50 Pts)
|
Diameter: 5.1 mm ± 0.1 mm | Surface Area: ~20.4 mm² | Classic balanced solitaire | — |
|
0.75 Carat (3/4 ct / 75 Pts)
|
Diameter: 5.8 mm ± 0.1 mm | Surface Area: ~26.4 mm² | — |
|
1.00 Carat (100 Points)
|
Diameter: 6.5 mm ± 0.1 mm | Surface Area: ~33.2 mm² | Universal engagement benchmark | — |
|
1.50 Carat (150 Points)
|
Diameter: 7.4 mm ± 0.1 mm | Surface Area: ~43.0 mm² | — |
|
2.00 Carat (200 Points)
|
Diameter: 8.1 mm ± 0.1 mm | Surface Area: ~51.5 mm² | Over 50% larger visual spread than 1.0ct | — |
|
3.00 Carat (300 Points)
|
Diameter: 9.4 mm ± 0.1 mm | Surface Area: ~69.4 mm² | — |
|
24 Karat Gold (24K)
|
— | 99.9% Pure Gold | Millesimal Hallmark: 999 | Soft, malleable, rich orange-yellow (too soft for daily rings) |
|
18 Karat Gold (18K)
|
— | 75.0% Pure Gold + 25% Copper/Silver/Zinc | Hallmark: 750 | European luxury standard, rich color, durable |
|
14 Karat Gold (14K)
|
— | 58.3%–58.5% Pure Gold + 41.5% Alloy | Hallmark: 585 (or 14K) | US engagement ring benchmark (~90% market share) |
|
10 Karat Gold (10K)
|
— | 41.7% Pure Gold + 58.3% Alloy | Hallmark: 417 (or 10K) | Minimum legal standard to be called 'gold' in the USA |
|
9 Karat Gold (9K)
|
— | 37.5% Pure Gold | Hallmark: 375 | Legal minimum gold standard in the UK, Australia, and South Africa |
|
Sterling Silver Standard
|
— | 92.5% Pure Silver + 7.5% Copper | Hallmark: 925 / STERLING | Balance gives silver tensile hardness |
|
Fine Platinum Standard
|
— | 95.0% Pure Platinum + 5% Ruthenium/Iridium | Hallmark: 950 / PLAT | Dense (21.45 g/cm³), hypoallergenic |