Carat Weight Calculator

Convert carat weights to grams, milligrams, ounces, pounds, and other units for precious stones and diamonds.

Essential tool for jewelers, gemologists, and precious stone enthusiasts. Convert between carats, grams, milligrams, ounces, and pounds with precision.

Examples

Click on any example to load it into the calculator.

1 Carat Diamond

Diamond

Standard 1 carat diamond weight conversion.

Carats: 1 ct

Grams: 0.2 g

Milligrams: 200 mg

Ounces: 0.00643 oz t

Pounds: 0.000441 lb

5 Carat Emerald

Emerald

Large emerald gemstone weight conversion.

Carats: 5 ct

Grams: 1 g

Milligrams: 1000 mg

Ounces: 0.03215 oz t

Pounds: 0.002205 lb

0.5 Carat Ruby

Ruby

Small ruby gemstone weight conversion.

Carats: 0.5 ct

Grams: 0.1 g

Milligrams: 100 mg

Ounces: 0.003215 oz t

Pounds: 0.0002205 lb

2.5 Carat Sapphire

Sapphire

Medium sapphire gemstone weight conversion.

Carats: 2.5 ct

Grams: 0.5 g

Milligrams: 500 mg

Ounces: 0.016075 oz t

Pounds: 0.0011025 lb

Other Titles
Understanding Carat Weight Calculator: A Comprehensive Guide
Master the art of gemstone weight measurement and conversion. Learn about carats, their history, and how to accurately convert between different weight units for precious stones.

What is the Carat Weight Calculator?

  • Definition and Purpose
  • Historical Background
  • Modern Applications
The Carat Weight Calculator is an essential tool for anyone working with precious stones, particularly diamonds and colored gemstones. It provides precise conversions between carats and other weight units, enabling accurate measurements for jewelry making, gemstone trading, and scientific analysis. The calculator serves as a bridge between the specialized world of gemology and standard measurement systems, ensuring consistency and accuracy in weight determinations.
The Carat: A Specialized Unit of Measurement
The carat (ct) is the standard unit for measuring gemstone weight, with one carat equaling exactly 0.2 grams or 200 milligrams. This precise definition was established in 1907 by the Fourth General Conference on Weights and Measures, replacing the variable carat weights that existed across different regions and gem markets. The carat's name derives from the carob seed, which was historically used as a reference weight due to its remarkable consistency in size and weight.
Historical Evolution of Carat Measurement
The carat system has ancient origins, with early civilizations using seeds, grains, and other natural objects as weight references. The carob seed (Ceratonia siliqua) became the standard reference in the Mediterranean region due to its consistent weight of approximately 0.2 grams. This natural consistency made it ideal for gemstone trading, where precise weight measurements were crucial for determining value. The modern metric carat was standardized to eliminate regional variations and ensure international consistency.
Contemporary Applications in Gemology
Today, the carat weight calculator serves multiple critical functions in the gemstone industry. Jewelers use it for precise stone sizing and setting calculations, gemologists employ it for scientific analysis and certification, and traders rely on it for accurate pricing and valuation. The calculator's precision is particularly important for diamonds, where even small weight differences can significantly impact value due to the exponential pricing structure based on carat weight.

Key Conversion Relationships:

  • 1 carat = 0.2 grams = 200 milligrams
  • 1 gram = 5 carats = 1000 milligrams
  • 1 troy ounce = 155.517 carats
  • 1 pound = 2267.96 carats

Step-by-Step Guide to Using the Carat Calculator

  • Input Selection and Entry
  • Calculation Process
  • Result Interpretation
Using the Carat Weight Calculator effectively requires understanding which input unit to use and how to interpret the results accurately. This systematic approach ensures precise conversions and helps avoid common measurement errors that can occur in gemstone work.
1. Choosing the Appropriate Input Unit
Select the input unit based on your available measurement. If you have a gemstone certificate or grading report, use the carat weight listed there. For rough stones or uncertified gems, you may need to weigh them in grams or milligrams using a precision scale. Choose the unit that provides the most accurate measurement for your specific situation, considering the precision of your measuring equipment and the size of the stone.
2. Entering Values with Proper Precision
Enter your weight value with appropriate decimal places. For carats, use up to three decimal places (e.g., 1.234 ct) as this is the standard precision in gemology. For grams, use up to four decimal places for small stones. For milligrams, whole numbers are typically sufficient. Ensure you're using the correct unit to avoid conversion errors that could significantly impact calculations.
3. Understanding and Using Results
The calculator provides conversions to all major weight units simultaneously. Use the carat value for gemstone pricing and certification, the gram value for scientific calculations, and the milligram value for very precise measurements. The troy ounce conversion is useful for precious metal comparisons, while the pound conversion helps with bulk calculations for larger stones or collections.
4. Verification and Cross-Checking
Always verify your results by checking that the conversions make logical sense. For example, if you enter 1 carat, you should see 0.2 grams, 200 milligrams, and so on. If results seem incorrect, double-check your input value and unit selection. For critical applications like diamond certification or high-value transactions, consider using multiple measurement methods to confirm accuracy.

Common Input Scenarios:

  • Diamond certificate: Use carat weight from GIA or other certification
  • Rough stone: Weigh in grams, convert to carats for pricing
  • Small gem: Use milligrams for precision, convert to carats
  • Bulk lots: Use pounds or ounces, convert to carats for individual pricing

Real-World Applications and Industry Uses

  • Jewelry Manufacturing
  • Gemstone Trading
  • Scientific Research
The Carat Weight Calculator serves as a fundamental tool across multiple industries and applications, from traditional jewelry making to modern scientific research and international trade.
Jewelry Design and Manufacturing
Jewelers rely on precise carat weight calculations for setting design, metal weight estimation, and pricing. When designing a ring with a 2-carat center stone, jewelers need to calculate the total metal weight, estimate setting costs, and determine the final price. The calculator helps ensure that all weight-related calculations are accurate, preventing costly errors in material estimation and pricing. For custom jewelry, precise weight conversions are essential for creating accurate CAD designs and 3D models.
Gemstone Trading and Valuation
In the international gemstone market, carat weight is the primary factor in determining value, especially for diamonds. Traders use the calculator to convert between different measurement systems used in various countries and markets. For example, some markets quote prices per gram for rough stones, while others use carats for cut stones. The calculator enables quick conversions for price comparisons and helps traders make informed decisions about purchases and sales.
Scientific Research and Gemology
Gemologists and researchers use precise weight measurements for scientific analysis, including density calculations, inclusion studies, and synthetic gemstone identification. The calculator's precision is crucial for these applications, where even small measurement errors can lead to incorrect conclusions. Research institutions use standardized weight conversions to ensure consistency across studies and to compare results from different laboratories worldwide.

Industry-Specific Applications:

  • Diamond certification: GIA, IGI, and other labs use precise carat measurements
  • Jewelry insurance: Accurate weight values for policy documentation
  • Custom jewelry: Precise weight calculations for CAD design and pricing
  • Gemstone mining: Converting bulk weights to individual stone values

Common Misconceptions and Best Practices

  • Weight vs Size Confusion
  • Precision Requirements
  • Unit Conversion Errors
Understanding common misconceptions about carat weight measurement helps ensure accurate calculations and prevents costly errors in gemstone work.
Myth: Carat Weight Equals Physical Size
A common misconception is that carat weight directly corresponds to physical size. While weight and size are related, they're not the same. Two stones of equal carat weight can have different dimensions depending on their cut, shape, and density. For example, a 1-carat round brilliant diamond typically measures about 6.5mm in diameter, but a 1-carat emerald-cut diamond might be 7mm long and 5mm wide. The calculator provides weight conversions but doesn't account for these dimensional variations.
Precision Requirements in Different Contexts
The required precision varies depending on the application. For diamond certification, weights are typically measured to three decimal places (e.g., 1.234 ct). For rough stone trading, two decimal places may be sufficient. For scientific research, four or more decimal places might be required. The calculator provides high precision, but users should understand the appropriate level of precision for their specific needs to avoid over-precision or under-precision errors.
Avoiding Unit Conversion Errors
Common conversion errors include confusing avoirdupois ounces with troy ounces, mixing metric and imperial units, and using outdated conversion factors. The calculator uses standardized conversion factors, but users should be aware of these potential pitfalls. For example, troy ounces (used for precious metals and gemstones) are different from avoirdupois ounces (used for general weight measurements), and using the wrong system can lead to significant errors.

Best Practice Guidelines:

  • Always verify measurements with certified scales and equipment
  • Use appropriate precision for your specific application
  • Understand the difference between weight and physical dimensions
  • Double-check conversions for high-value transactions

Mathematical Derivation and Conversion Formulas

  • Conversion Factor Derivation
  • Precision Calculations
  • Statistical Analysis
The mathematical foundation of carat weight conversion is based on precise international standards and scientific measurements that ensure consistency across global markets and applications.
The Metric Carat Definition
The modern metric carat is defined as exactly 0.2 grams (200 milligrams). This definition was established by the Fourth General Conference on Weights and Measures in 1907 and has been maintained by the International Bureau of Weights and Measures (BIPM). The conversion factors used in the calculator are derived from this fundamental definition: 1 carat = 0.2 grams = 200 milligrams. This precise definition eliminates the historical variations that existed between different regional carat standards.
Conversion Factor Calculations
All conversion factors in the calculator are mathematically derived from the base carat definition. For example, to convert carats to troy ounces: 1 troy ounce = 31.1035 grams, so 1 carat = 0.2 grams ÷ 31.1035 grams/troy ounce = 0.00643 troy ounces. For pounds: 1 pound = 453.592 grams, so 1 carat = 0.2 grams ÷ 453.592 grams/pound = 0.000441 pounds. These calculations ensure mathematical precision and consistency across all conversions.
Precision and Rounding Considerations
The calculator maintains appropriate precision for each unit based on typical usage in the gemstone industry. Carat weights are displayed to three decimal places (standard for gemology), grams to four decimal places, milligrams as whole numbers, and troy ounces to five decimal places. The rounding is performed using standard mathematical rules to ensure accuracy while maintaining practical usability. For scientific applications requiring higher precision, the underlying calculations can be extended to additional decimal places.

Mathematical Relationships:

  • 1 ct = 0.2 g = 200 mg = 0.00643 oz t = 0.000441 lb
  • 1 g = 5 ct = 1000 mg = 0.03215 oz t = 0.002205 lb
  • 1 oz t = 155.517 ct = 31.1035 g = 31,103.5 mg = 0.06857 lb
  • 1 lb = 2267.96 ct = 453.592 g = 453,592 mg = 14.5833 oz t