Carat Converter

A carat converter is a tool that translates the carat (ct) measurement—used primarily for gemstones and pearls—into other mass units such as grams, milligrams, ounces, grains, and points. The carat is the universal standard for weighing precious stones, and understanding its relationship to other mass units is essential for jewelers, gemologists, and consumers purchasing diamonds and gemstones.

One carat is defined as exactly 0.2 grams (200 milligrams). This metric carat standard was adopted internationally in 1913 and is maintained by the Gemological Institute of America (GIA) and other gemological organizations worldwide. The carat provides a precise, universally understood way to express gemstone weight, regardless of the stone's shape, cut, or type.

The term "carat" derives from the carob seed, which ancient traders used as a reference weight because of its remarkable uniformity. Today, the modern metric carat is precisely standardized, making it the foundation of the gemstone industry's pricing, grading, and trading systems.

This converter allows you to enter any carat value and instantly see the equivalent in grams, milligrams, ounces, grains, and points (where 1 carat = 100 points). This is useful for comparing gemstone specifications, understanding jewelers' terminology, and converting between measurement systems used in different markets.

The carat is precisely defined in terms of the metric system: 1 carat equals exactly 0.2 grams. From this definition, all other carat conversions are derived through simple multiplication.

Grams: Multiply carats by 0.2 to get grams. Since there are 5 carats in a gram, dividing the carat value by 5 gives the same result.

Milligrams: Multiply carats by 200 to get milligrams. This is useful for very small stones where milligrams provide more precision.

Points: Multiply carats by 100. Jewelers often express diamond weight in points for stones under 1 carat, so a 0.50-carat diamond is described as a "50-point diamond."

Grains: Multiply carats by approximately 3.08647. The grain is an older unit still used in some gem trading traditions.

Ounces: Multiply carats by approximately 0.00705479. This is less common in gemology but useful for converting to standard imperial measurements.

This carat converter provides instant multi-unit conversion:

1. Enter the Carat Value: Type the weight of your gemstone in carats into the input field. You can use decimal values—for example, 0.75 for a three-quarter carat stone.
2. View the Gram Equivalent: The primary result shows the weight in grams, which is the most common alternative to carats in the metric system.
3. Review All Conversions: Below the primary result, the calculator displays the weight in milligrams, points, and grains simultaneously, giving you a complete conversion reference.

The quick reference section shows common conversions and notable diamond weights for context.

The calculator output provides five different representations of the same weight. The gram equivalent is the most useful for general purposes, as it relates the carat to the familiar metric system. The milligram equivalent provides greater precision for very small stones.

The point equivalent is important in diamond retail. Diamonds under 1 carat are commonly described by their point weight. A 0.75-carat diamond is a "75-pointer," a 0.50-carat diamond is a "50-pointer," and so on. This terminology is standard in the diamond trade.

The grain equivalent connects to historical measurement systems still occasionally referenced in pearl and antique gemstone trading. The ounce equivalent provides a bridge to imperial measurements, though this is less common in gemology.

Diamond purchasing relies heavily on carat weight as one of the four Cs (carat, color, clarity, cut). Understanding carat equivalents helps consumers compare diamonds across listings and grasp the actual size and weight of stones they are considering purchasing.

Jewelry design requires precise weight calculations for setting stones, estimating material costs, and creating balanced designs. Converting between carats and grams helps jewelers plan settings and estimate the total weight of finished pieces.

Insurance appraisals need accurate weight specifications. Appraisers document gemstone weights in carats and may need to convert to other units for international clients or insurance documentation that requires metric specifications.

Gemological laboratory reports from organizations like GIA, AGS, and IGI report gemstone weight in carats. Understanding the relationship to other units helps consumers and trade professionals interpret these reports and compare specifications across different grading systems.