Carat (ct) - Unit Information & Conversion
🔄 Quick Convert Carat
What is a Carat?
The carat is a unit of mass equal to exactly 200 milligrams (0.2 grams) used exclusively for measuring the weight of gemstones (diamonds, rubies, sapphires, emeralds) and pearls in the jewelry industry. Not to be confused with "karat" (the measure of gold purity), the carat derives from the ancient practice of using carob seeds as counterweights on balance scales, as these seeds were believed to have remarkably uniform weight. The modern metric carat of 200 mg was standardized internationally at the Fourth General Conference on Weights and Measures in Paris (1907) and adopted by major diamond trading centers (Antwerp, London, New York) by 1914, replacing various national standards that ranged from 188-215 mg. Carat weight is the most objective of the "Four Cs" used to evaluate diamonds (carat, cut, color, clarity), directly determining a gemstone's size and significantly influencing its value—though price per carat increases exponentially with size due to the rarity of larger stones. A one-carat diamond weighs 200 mg and measures approximately 6.5mm in diameter (for a standard round brilliant cut), while famous diamonds like the Cullinan (3,106 carats rough, largest ever found) or the Hope Diamond (45.52 carats) demonstrate the extraordinary scale and value concentrated in these precisely measured units.
History of the Carat
The word "carat" traces to the Greek "keration" (κεράτιον), meaning "carob seed," from the carob tree (Ceratonia siliqua) native to the Mediterranean. Ancient merchants from Greece, Rome, and the Middle East used dried carob seeds as counterweights on balance scales when measuring precious stones and metals, believing these seeds had uniform weight (~200 mg, remarkably close to the modern standard). This practice spread along trade routes connecting Mediterranean, Middle Eastern, and Asian gem markets throughout antiquity and the Middle Ages. However, carob seeds actually vary by 10-20% in weight, and different regions developed divergent carat standards: the Ottoman Empire used slightly heavier carats, India had various local measures, and European nations each defined their own carat (the "Florentine carat," "Amsterdam carat," "Paris carat," etc., ranging from 188-215 mg). This inconsistency caused confusion in international gem trade, with disputes over weight and value. The modern era of standardization began in the late 19th century as global commerce expanded. In 1907, the Fourth General Conference on Weights and Measures (CGPM) in Paris adopted the metric carat at exactly 200 milligrams, proposed by international gem traders and jewelers seeking uniformity. Major diamond centers—Antwerp (Belgium), London (UK), and New York (USA)—officially adopted the 200 mg standard by 1914. The United States codified it in law in 1913. This standardization revolutionized the diamond industry, enabling precise international pricing, consistent grading, and transparent trade. Today, the carat is legally defined worldwide and enforced by national metrology institutes, ensuring that a one-carat diamond in Mumbai weighs exactly the same as in Antwerp or New York.
Quick Answer
1 carat (ct) = 200 milligrams = 0.2 grams = 0.00705479 ounces
A carat is the standard unit for measuring gemstone weight. A one-carat diamond weighs 200 mg and is approximately 6.5 mm in diameter (for a round brilliant cut).
Important: Carat (ct) measures gemstone weight, not gold purity. Gold purity is measured in karats (K or kt), where 24K = pure gold.
Quick Comparison Table
| Weight Unit | Equals 1 Carat |
|---|---|
| Milligrams (mg) | 200 mg (exactly) |
| Grams (g) | 0.2 g (exactly) |
| Ounces (oz) | 0.00705479 oz |
| Pounds (lb) | 0.00044092 lb |
| Kilograms (kg) | 0.0002 kg |
Gemstone Size Reference (Round Brilliant Cut Diamonds):
- 0.25 carat: ~4 mm diameter
- 0.50 carat: ~5.1 mm diameter
- 1.00 carat: ~6.5 mm diameter
- 2.00 carats: ~8.2 mm diameter
- 3.00 carats: ~9.3 mm diameter
- 5.00 carats: ~11 mm diameter
Points (Common Trade Terminology):
- 1 carat = 100 points
- 0.50 carat = 50 points ("fifty-pointer")
- 0.75 carat = 75 points
Definition
A carat (symbol: ct) is a unit of mass used exclusively for measuring gemstones and pearls, defined as:
1 carat = 200 milligrams (mg) = 0.2 grams (g)
Carat vs. Karat: Critical Distinction
Carat (ct) = Gemstone weight
- Measures mass of diamonds, rubies, sapphires, emeralds, pearls, etc.
- 1 ct = 200 mg
Karat (K or kt) = Gold purity
- Measures proportion of pure gold in an alloy
- 24K = 100% pure gold
- 18K = 75% gold (18/24)
- 14K = 58.3% gold (14/24)
Spelling/Pronunciation:
- United States: "Carat" (gemstones), "Karat" (gold) - different spellings
- UK/Commonwealth: Often "carat" for both, distinguished by context (ct vs. K)
- Pronunciation: Both pronounced identically ("CARE-ut")
Example: An 18-karat gold ring set with a 2-carat diamond contains gold that is 75% pure and a diamond weighing 400 mg.
Points: The Carat Subdivision
In the gem trade, carats are divided into 100 points:
- 1 carat = 100 points
- 0.01 carat = 1 point
Trade Terminology:
- "50-pointer" = 0.50 carat (50 points)
- "Three-quarter carat" = 0.75 ct (75 points)
- "10-point diamond" = 0.10 ct
Points allow precise specification of smaller gemstones and enable pricing granularity.
History of the Carat
Ancient Origins: Carob Seeds (c. 3000 BCE - 500 CE)
The Carob Tree:
- Carob tree (Ceratonia siliqua): Native to Mediterranean region
- Produces seed pods containing small, hard seeds
- Ancient belief: Carob seeds had remarkably uniform weight (~200 mg)
Early Use as Weights:
- Ancient Greece: Used carob seeds ("keration") as counterweights on balance scales
- Roman Empire: Adopted Greek practice for weighing gems, gold, medicines
- Middle East & India: Arab and Indian merchants used carob or similar seeds
- Reason: Small, portable, abundant, believed to be consistent
Reality Check: Modern analysis shows carob seeds actually vary by 10-20% in weight (180-220 mg), so ancient measurements weren't as precise as believed. However, the average (~200 mg) remarkably matches the modern standard.
Medieval to Early Modern Period (500-1800 CE)
Divergent Regional Standards: As gem trade expanded across Europe, Middle East, and Asia, different regions developed local carat standards:
European Carats:
- Florence (Italy): ~197 mg
- Amsterdam (Netherlands): ~205.3 mg
- Paris (France): ~205 mg
- London (UK): ~205.3 mg
- Venice (Italy): ~207 mg
Ottoman Empire:
- Constantinople carat: ~200-205 mg (varied over time)
India:
- Mangelin (Madras): ~193 mg
- Rati: Ancient Indian unit (~188 mg), still used traditionally for pearls
Problems:
- International gem trade faced confusion: "Is this a Florence carat or Amsterdam carat?"
- Disputes over weight and pricing
- Fraudulent practices exploiting different standards
The Diamond Revolution (1800s)
South African Diamond Discoveries (1867-1870s):
- Discovery of diamonds at Kimberley, South Africa
- Massive increase in diamond supply
- Rise of industrial diamond mining
- Expansion of international diamond trade
De Beers Consolidation:
- Cecil Rhodes founded De Beers Mining Company (1888)
- Consolidated South African diamond production
- Established control over global diamond supply
- Created need for international weight standard
Growing Trade Complexity:
- Diamonds moved from South Africa → London → Antwerp → New York → global markets
- Multiple carat standards caused pricing inconsistencies
- Insurers, traders, cutters demanded standardization
International Standardization (1907-1914)
Fourth General Conference on Weights and Measures (1907):
- Convened in Paris to expand metric system
- International gem trade representatives advocated for uniform carat
- Proposal: Define carat as exactly 200 milligrams
- Rationale: Close to existing averages, clean metric value
Advantages of 200 mg:
- Simple metric conversion: 5 carats = 1 gram
- Close to historical average: Most European carats were 197-207 mg
- No major disruption: Minimal adjustment for major markets
- Decimal-friendly: Easy calculation and subdivision
Global Adoption:
- 1907: Metric carat adopted at CGPM Paris
- 1913: United States codified 200 mg carat in federal law
- 1914: Antwerp (Belgium), London (UK), New York officially adopted
- 1920s-1930s: Remaining gem centers transitioned
- By 1950s: Universal acceptance worldwide
The Modern Diamond Industry (1930s-Present)
The "Four Cs" Framework (1940s):
- Gemological Institute of America (GIA) established 1931
- Robert M. Shipley (GIA founder) popularized diamond grading
- 1940s: GIA codified the "Four Cs" of diamond quality:
- Carat (weight)
- Cut (proportions, symmetry, polish)
- Color (D-to-Z scale, D = colorless)
- Clarity (internal inclusions, external blemishes)
Carat as Primary Value Driver:
- Of the Four Cs, carat weight is most objective (precise scale measurement)
- Cut, color, clarity require expert judgment
- Carat directly determines size (larger diamonds rarer, more valuable)
- Price per carat increases exponentially with weight
Diamond Certification:
- GIA, International Gemological Institute (IGI), and others issue certificates
- Certificates specify carat weight to 0.01 ct precision
- Example: "1.27 carats" (127 points), measured to ±0.005 ct accuracy
Electronic Precision Scales:
- Modern gem scales measure to 0.001 carat (0.2 mg precision)
- Temperature-controlled environments ensure accuracy
- Calibrated against reference standards traceable to SI kilogram
Contemporary Developments (1990s-Present)
Synthetic Diamonds:
- Lab-grown diamonds (HPHT, CVD methods) entered market
- Sold by carat, like natural diamonds
- Price typically 30-70% less than natural for same carat weight
Online Diamond Trade:
- Internet sellers (Blue Nile, James Allen, etc.) list specifications including exact carat weight
- Photos, videos, 360° views help buyers assess size
- Carat weight filtering standard on all sites
Famous Large Diamonds:
- Modern discoveries and sales emphasize carat weight as headline figure
- "Largest diamond found in 100 years: 1,109 carats!"
Real-World Examples of Carats in Action
1. The Four Cs: Carat Weight in Diamond Valuation
Carat as the Most Objective Measure:
Of the Four Cs, carat weight is precisely measurable, while cut, color, and clarity involve expert judgment:
Example Diamond Comparison:
| Specification | Diamond A | Diamond B |
|---|---|---|
| Carat | 1.00 ct | 2.00 ct |
| Cut | Excellent | Excellent |
| Color | G (near-colorless) | G (near-colorless) |
| Clarity | VS1 (very slightly included) | VS1 |
| Price | $6,000 | $28,000 |
Why is Diamond B not 2× the price?
- Larger diamonds are exponentially rarer
- Price per carat increases with size
- Diamond A: $6,000 per carat
- Diamond B: $14,000 per carat (2.33× higher per-carat price)
Magic Sizes: Certain carat weights command premiums due to psychological desirability:
- 0.50 ct ("half-carat"): Popular engagement ring size
- 1.00 ct ("one-carat"): Psychologically significant threshold
- 2.00 ct, 3.00 ct, 5.00 ct: Major milestones
Just Below Magic Sizes: Smart buyers may purchase 0.90 ct instead of 1.00 ct:
- Visually indistinguishable (~0.2 mm difference)
- Price savings: 15-20% per carat
- Example: 0.95 ct diamond may cost $5,000; 1.05 ct may cost $7,000
2. Famous Diamonds and Their Carat Weights
The Cullinan Diamond (1905):
- Largest gem-quality diamond ever found: 3,106.75 carats rough
- Discovered in South Africa, presented to King Edward VII
- Cut into 9 major stones and 96 smaller brilliants:
- Cullinan I ("Great Star of Africa"): 530.2 carats (largest cut colorless diamond)
- Cullinan II: 317.4 carats
- Both in British Crown Jewels
The Hope Diamond:
- 45.52 carats (deep blue, famous "cursed" diamond)
- Currently in Smithsonian National Museum of Natural History
- Valued at $200-250 million
The Koh-i-Noor:
- 105.6 carats (currently in British Crown Jewels)
- Originally 186 carats before recutting (1852)
- Controversy over ownership (India, Pakistan, UK claims)
The Golden Jubilee:
- 545.67 carats (largest cut and faceted diamond)
- Fancy yellow-brown color
- Thai Royal Family
The Pink Star:
- 59.60 carats (largest internally flawless fancy vivid pink diamond)
- Sold at Sotheby's Hong Kong (2017) for $71.2 million (~$1.2 million per carat!)
Modern Large Discoveries:
- Lesedi La Rona (2015, Botswana): 1,109 carats rough
- Sewelô (2019, Botswana): 1,758 carats rough
3. Engagement Ring Market
Average Engagement Ring Sizes (US, 2020s):
- Average carat weight: ~1.0-1.2 carats (center stone)
- Median: ~0.75-1.0 carat (many below average due to high-end outliers)
- Price range: $3,000-$10,000 (varies widely by quality)
Regional Variations:
- United States: 1.0-1.5 ct average
- Europe: 0.5-1.0 ct average (smaller traditional preference)
- Asia (China, Japan): 0.5-0.8 ct average
- Middle East: 1.5-3.0 ct average (larger stones culturally valued)
Celebrity Engagement Rings (Carat Weights):
- Kim Kardashian (from Kanye West): 15 carats (cushion cut)
- Beyoncé (from Jay-Z): 18 carats (emerald cut)
- Jennifer Lopez (from Alex Rodriguez): 15 carats (emerald cut)
- Mariah Carey (from James Packer): 35 carats (emerald cut)
- Elizabeth Taylor (from Richard Burton): 33.19 carats (Krupp diamond)
These celebrity examples showcase the aspirational aspect of large carat weights in popular culture.
4. Colored Gemstones: Carat and Density
Different Gemstones, Same Carat, Different Sizes:
Gemstones have different densities (specific gravity), so 1 carat of different stones has different volumes:
| Gemstone | Specific Gravity | 1-Carat Diameter (approx.) |
|---|---|---|
| Diamond | 3.52 | 6.5 mm |
| Ruby | 4.00 | 6.0 mm (smaller than diamond) |
| Sapphire | 4.00 | 6.0 mm (smaller than diamond) |
| Emerald | 2.71 | 6.9 mm (larger than diamond) |
| Aquamarine | 2.68 | 7.0 mm (larger than diamond) |
| Opal | 2.15 | 7.5 mm (larger than diamond) |
Implication: A 1-carat emerald looks larger than a 1-carat diamond because emerald is less dense.
Gemstone Pricing Differences:
- Diamonds: ~$3,000-$20,000+ per carat (depending on quality)
- Ruby (high quality): $1,000-$15,000+ per carat
- Sapphire (high quality): $500-$10,000+ per carat
- Emerald (high quality): $500-$10,000+ per carat
- Aquamarine: $100-$500 per carat
- Amethyst: $10-$50 per carat
5. Pearls: Carat Weight and Grading
Pearls Measured by Carat: While pearls are often measured by millimeter diameter, they're also weighed in carats for trade:
Pearl Types:
- Akoya pearls (Japan): 2-10 mm, ~0.25-2 carats
- South Sea pearls (Australia, Philippines): 10-20 mm, ~2-10 carats
- Tahitian pearls (French Polynesia): 8-16 mm, ~1-5 carats
- Freshwater pearls (China): 2-15 mm, ~0.1-3 carats
La Peregrina Pearl:
- Famous pear-shaped pearl: 55.95 carats
- Owned by Spanish royalty, later Elizabeth Taylor
- Sold at Christie's (2011) for $11.8 million
6. Synthetic and Lab-Grown Diamonds
Lab-Grown Diamond Market (2020s):
- Chemically identical to natural diamonds
- Sold by carat, same grading standards
- Price: 30-70% less than natural diamonds
- Example: 1-carat lab-grown (excellent cut, G color, VS1 clarity) ~$1,500-$3,000 vs. natural ~$5,000-$8,000
Largest Lab-Grown Diamonds:
- Technology improving rapidly
- 10+ carat lab-grown stones now producible
- Market focuses on quality, not just size
7. Investment Diamonds
Diamonds as Assets:
- Some investors buy diamonds as stores of value
- Focus on larger sizes (2+ carats), high quality (D-F color, IF-VVS clarity)
- Liquidity lower than gold, but rare stones hold value
Pink and Blue Diamonds:
- Fancy color diamonds trade at enormous premiums
- Pink diamonds (Argyle mine, Australia, now closed): $50,000-$200,000+ per carat
- Blue diamonds: $100,000-$400,000+ per carat (rare)
Common Uses of the Carat in Modern Contexts
1. Jewelry Retail and E-Commerce
Every jewelry store and online retailer specifies carat weight:
- Product listings: "1.5 ct Diamond Solitaire Ring"
- Filters: Search by carat range (0.5-0.75 ct, 0.75-1.0 ct, etc.)
- Pricing: Often listed as "price per carat"
- Certification: GIA, IGI certificates state precise carat weight
Example Product Description:
"18K White Gold Engagement Ring featuring a 1.27 ct Round Brilliant Cut Diamond (G color, VS2 clarity, Excellent cut) with 0.25 ct total weight of side stones."
2. Gemological Laboratories
Institutions like GIA, IGI, AGS (American Gem Society) issue certificates:
- Carat weight: Measured to 0.01 ct precision
- Measurement: Length, width, depth in millimeters
- Report number: Unique identifier
- Laser inscription: Microscopic certificate number on diamond girdle
Certificate ensures:
- Buyer knows exact weight
- Seller can't misrepresent size
- International trade transparency
3. Auction Houses and High-Value Sales
Christie's, Sotheby's, and other auction houses emphasize carat weight:
- Lot descriptions: "Lot 345: 10.12 ct Fancy Vivid Blue Diamond Ring"
- Estimates: "$2-3 million" (often $200,000-$500,000 per carat for rare colors)
- Hammer prices: Record sales widely reported by carat
Recent Record Sales:
- Pink Star (59.60 ct): $71.2 million (2017) = $1.195 million/ct
- Oppenheimer Blue (14.62 ct): $57.5 million (2016) = $3.93 million/ct
4. Mining and Rough Diamond Trade
Diamond mines report production in carats:
- Botswana (Debswana mines): ~23 million carats annually
- Russia (Alrosa): ~28 million carats annually
- Canada (Diavik, Ekati): ~6 million carats annually
Rough Diamond Pricing:
- Sold by carat at rough diamond exchanges (Antwerp, Dubai, Mumbai)
- Average rough prices: $50-$150 per carat (varies by quality)
- High-quality rough: $300-$500+ per carat
5. Customs and Import/Export
International gem trade requires carat weight declarations:
- Harmonized System (HS) codes: Classify gems by type and weight
- Import duties: Often based on declared carat weight and value
- Kimberley Process Certification: Anti-conflict diamond scheme specifies carat weight
Example: Importing 1,000 ct of rough diamonds into EU requires documentation with precise weight.
6. Insurance and Appraisals
Jewelry insurance policies specify carat weight:
- Appraisal: "1.52 ct center stone, 0.40 ct total side stones"
- Replacement value: Based on carat × price-per-carat for quality
- Loss claims: Carat weight determines payout
Example Policy: "Insured item: Platinum ring with 2.03 ct diamond (H color, VS1). Replacement value: $18,000. Annual premium: $180 (1% of value)."
7. Consumer Education and Marketing
Jewelry retailers educate customers using the Four Cs:
- In-store displays: Charts showing carat sizes
- Online tools: Interactive "build your ring" showing carat options with price updates
- Marketing: "50% larger diamond for only 30% more!" (e.g., 0.75 ct vs. 0.50 ct)
De Beers "A Diamond is Forever" Campaign:
- Emphasized carat size as symbol of commitment
- "Two months' salary" guideline (now ~one month average)
How to Convert Carats to Other Weight Units
Basic Conversion Formulas
1 carat = 200 milligrams (mg) - EXACT
1 carat = 0.2 grams (g) - EXACT
1 carat = 0.0002 kilograms (kg) - EXACT
1 carat = 0.00705479 ounces (oz)
1 carat = 0.00044092 pounds (lb)
Reverse:
1 gram = 5 carats (EXACT)
1 kilogram = 5,000 carats
1 ounce = 141.748 carats
1 pound = 2,267.96 carats
Carat subdivisions:
1 carat = 100 points
1 point = 0.01 carat = 2 milligrams
Carats ↔ Other Weight Units
| From | To | Multiply by |
|---|---|---|
| Carats | Milligrams | × 200 |
| Carats | Grams | × 0.2 (or ÷ 5) |
| Carats | Kilograms | × 0.0002 (or ÷ 5,000) |
| Carats | Ounces | × 0.00705479 |
| Carats | Pounds | × 0.00044092 |
| Milligrams | Carats | ÷ 200 |
| Grams | Carats | × 5 |
| Ounces | Carats | × 141.748 |
Examples
Example 1: Engagement Ring
- Center diamond: 1.25 carats
- Side stones: 0.30 carats total
- Total diamond weight: 1.25 + 0.30 = 1.55 carats
- Convert to grams: 1.55 × 0.2 = 0.31 grams
- Convert to milligrams: 1.55 × 200 = 310 milligrams
Example 2: Famous Diamond (Hope Diamond)
- Weight: 45.52 carats
- Convert to grams: 45.52 × 0.2 = 9.104 grams
- Convert to ounces: 45.52 × 0.00705479 = 0.321 ounces
Example 3: Points to Carats
- Diamond advertised as "75-pointer"
- 75 points = 75/100 = 0.75 carats
- In milligrams: 0.75 × 200 = 150 mg
Example 4: Bulk Gemstones
- Gemstone dealer has 500 grams of small sapphires
- Convert to carats: 500 × 5 = 2,500 carats
Example 5: Mining Production
- Mine produces 10 million carats of rough diamonds annually
- Convert to kilograms: 10,000,000 × 0.0002 = 2,000 kg (2 metric tons)
- Convert to pounds: 10,000,000 × 0.00044092 = 4,409 pounds
Common Conversion Mistakes to Avoid
1. ❌ Confusing Carat with Karat
Mistake: "This 18-carat gold ring is very heavy."
Problem: Karat (gold purity) is confused with carat (gemstone weight).
✅ Correct:
- "18-karat gold ring" (18K = 75% pure gold)
- "2-carat diamond ring" (diamond weighs 400 mg)
- Combined: "18-karat gold ring with a 2-carat diamond"
Mnemonic: Carat = Ct = gemstone weight; Karat = K = gold purity.
2. ❌ Assuming Larger Carat = Always Better
Mistake: "A 2-carat diamond is automatically worth more than a 1-carat diamond."
Problem: Cut, color, and clarity also determine value. Poor-quality 2 ct may be worth less than excellent 1 ct.
✅ Correct:
- 2 ct, J color (slightly yellow), SI2 clarity (visible inclusions), poor cut: ~$6,000
- 1 ct, D color (colorless), VVS1 clarity (nearly flawless), excellent cut: ~$12,000
Rule: Carat is one of Four Cs. All matter.
3. ❌ Confusing Carat Weight with Size (mm)
Mistake: "All 1-carat diamonds are 6.5 mm diameter."
Problem: Only true for well-cut round brilliant diamonds. Shallow or deep cuts have different diameters. Fancy shapes (oval, princess, pear) differ.
✅ Correct:
- 1 ct well-cut round brilliant: ~6.5 mm
- 1 ct shallow round: ~7.0 mm (spread out, but less sparkle)
- 1 ct deep round: ~6.0 mm (looks smaller, light leaks)
- 1 ct oval: ~7.7 × 5.7 mm (looks larger than round)
4. ❌ Using Imprecise Conversion Factors
Mistake: "1 carat = 0.2 grams, so 5 carats = 1.1 grams."
Problem: 5 × 0.2 = 1.0 gram, not 1.1. Simple arithmetic error.
✅ Correct: 5 carats = exactly 1 gram (5 × 0.2 = 1.0).
5. ❌ Ignoring Density Differences Between Gemstones
Mistake: "A 1-carat ruby is the same size as a 1-carat diamond."
Problem: Ruby is denser (SG 4.0) than diamond (SG 3.52), so 1 ct ruby is smaller (~6.0 mm vs. 6.5 mm).
✅ Correct: Same carat weight in different gemstones = different sizes due to density.
6. ❌ Confusing Total Carat Weight (TCW) with Center Stone Weight
Mistake: "This ring is 2 carats." (Referring to total weight including small side stones)
Problem: Center stone might be only 1.5 ct, with 0.5 ct in side stones. Jewelry ads often emphasize TCW.
✅ Correct: Specify center stone separately: "1.5 ct center diamond, 2.0 ct total weight."
Carat Conversion Formulas
To Kilogram:
To Gram:
To Milligram:
To Pound:
To Ounce:
To Stone:
To Ton (metric):
To Ton (US):
To Ton (UK):
To Microgram:
To Slug:
To Troy Ounce:
To Pennyweight:
To Grain:
To Dram:
To Quintal:
To Atomic Mass Unit:
To Pavan (India):
To Kati (India):
To Masha (India):
To Dina (India):
To Pras (India):
To Lota (India):
Frequently Asked Questions
There are exactly 200 milligrams (mg) in 1 carat (ct). This precise definition was adopted internationally in 1907 at the Fourth General Conference on Weights and Measures in Paris and has been the global standard ever since. The 200 mg figure was chosen because it was close to the average of various historical carat standards (which ranged from 188-215 mg across different regions) and because it creates a clean metric conversion: 5 carats = 1 gram. Modern gemological laboratories use precision electronic scales that can measure to 0.001 carat (0.2 mg) accuracy, ensuring consistent and transparent gem trade worldwide. For comparison, a US dollar bill weighs approximately 1 gram = 5 carats, and a paperclip weighs ~1 gram = 5 carats. The 200 mg standard is legally enforced by metrology institutes in all countries, making carat weight the most objective and reliable of the "Four Cs" of diamond grading.
Convert Carat
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