Carat (Weight) vs. Karat (Purity)
Carat (with a 'C') is a unit of mass used for diamonds and gemstones (1 ct = 0.200 grams). Karat (with a 'K') is a measure of gold purity (24K = 100% pure gold).
Carat vs. Karat Quick Reference
| Feature | Carat (ct) | Karat (k / kt) |
|---|---|---|
| What it Measures | Mass / Weight | Purity / Proportion |
| Standard Definition | 1 ct = exactly 200 milligrams (0.2 grams) | Fraction of 24 parts pure gold (e.g. 18/24 = 75%) |
| Origin | Carob seed (ancient Mediterranean weight standard) | Ancient Roman coin siliqua (1/24th of solidus) |
| Used For | Diamonds, Emeralds, Rubies, Sapphires, Pearls | Gold jewelry, Bullion bars, Coins, Watches |
| Common Values | 0.5 ct, 1.0 ct, 1.5 ct, 2.0 ct, 5.0 ct | 24K, 22K, 18K, 14K, 10K |
Why 24 Karats?
Gold purity is divided into 24 parts. 24K means 24 out of 24 parts are pure gold ($99.9\%$). Pure gold is too soft for rings, so it is alloyed with copper and silver to create durable 18K (75%) or 14K (58.3%) jewelry.
Diamond "Points" System
1 Carat is divided into 100 points. A "50-point diamond" weighs exactly 0.50 carats ($0.100\text{ grams}$). Diamond prices jump exponentially at full carat thresholds (1.00 ct, 2.00 ct).
🔗 Related Gemstone & Bullion Converters
Calculating fine gold scrap or melt values for jewelry? Assess alloy purity with our Gold Karat & Fine Melt Weight Calculator. For traditional South Asian bullion bars, convert tolas directly using our Tola to Grams Gold Converter, or review precious coin standards in our Troy Ounce vs Regular Ounce Guide.
Convert general grams and milligrams with Grams to Ounces or explore live equivalence across all 19 units on our Live Conversion Matrix and Universal Converter. International gemological standards (GIA, CGPM 1907) are detailed in our Scientific Methodology.