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Diamond Carat Weight Guide: Understanding Size with Carat & MM

Accurate Precious Metals

November 1, 2023

Unlock the Secret of Converting Diamond Size from Millimeters to Carats: Your Comprehensive Buying Guide

Measuring the carat weight of diamonds and gemstones can seem challenging, especially if you’re stuck with millimeter measurements. Don’t fret! This comprehensive guide will shed light on how to convert from millimeters (mm) to carats, thus empowering you with precise knowledge to choose the perfect gemstone or diamond for your next engagement ring or precious piece of jewelry. This article is a must-read if you want to make an informed and accurate decision about buying diamonds based on their actual size and carat weight.

  • Understand the difference between carats and millimeters and why it is vital in diamond or gemstone purchase
  • Learn the formula to estimate the weight of a diamond from its size in millimeters
  • Get acquainted with the diamond size chart and how to use it for carat weight estimation
  • Discover how diamond cut and shape can affect perceived size and weight
  • Find out how to choose the best diamond based on carat weight and size

What are Carats and How do they Relate to Diamond Size?

Simply put, a carat is a unit of weight used for gemstones and diamonds. When you hear someone referring to a 1-carat diamond, they’re speaking of a diamond that weighs 200 milligrams or 0.2 grams. However, it’s not as simple as relating weight to size. Two diamonds can have the same carat weight but look different in size. This is because the visual size of a diamond is often affected by its cut and shape. Also worth noting is that carats are divided into 100 points for finer measurements.

On the other hand, millimeters (mm) are a unit of measurement for length or size. When it comes to diamonds or gemstones, the millimeter measurement usually refers to the stone’s diameter or dimensions. But, remember, the size in mm does not directly translate to the weight in carats because of factors like cut and shape. Therefore, knowing how to convert from mm to carat weight can be essential when you are aiming to understand the actual size of a diamond.

How to Estimate the Carat Weight from Millimeters?

Estimating the carat weight from the dimensions of a diamond requires a simple formula. However, this method gives you an estimate, not the exact weight, as the diamond’s cut and proportions can affect the weight. But, it will still provide you with a rough idea about the weight of a diamond from its measurement in millimeters.

Here’s how you can estimate the weight: first, measure the diameter of the diamond in millimeters. Then, square this number and multiply it by the height of the diamond, also measured in millimeters. Last, multiply this result by the specific gravity of the diamond, which is 3.52. The result is the approximate carat weight of the diamond. However, keep in mind that this is just a rough estimation and can vary based on the diamond’s actual proportions and shape.

Using a Diamond Size Chart to Estimate Carat Weight

A diamond size chart can be a handy tool to estimate the carat weight of a diamond based on its size in millimeters. The chart lists the average diameters for different diamond cuts and their corresponding weight in carats. It can give you a visual idea of how big a diamond of a specific carat weight may appear when viewed from the top.

For example, a 1-carat round brilliant cut diamond is approximately 6.5 mm in diameter, and a 1-carat princess cut diamond would be about 5.5 mm. However, remember that these are average sizes, and actual sizes can vary based on the diamond’s proportions and cut quality. Understanding the diamond size chart will help you make more informed decisions when choosing a diamond based on carat size and shape.

How does the Cut of a Diamond Affect its Size and Weight?

The cut of a diamond plays a crucial role in determining its visual size and carat weight. Diamonds cut to ideal proportions will sparkle more and can appear larger than their actual carat weight. For instance, a round brilliant cut diamond maximizes light return and often appears larger than other diamond cuts of the same carat weight.

Conversely, diamonds with a deep cut can have a smaller diameter and appear smaller than their actual weight, while those with a shallow cut can have a larger diameter but may lack brilliance and sparkle. Therefore, the cut quality can significantly impact the appearance of a diamond, influencing its perceived size and weight.

How to Choose the Best Diamond Based on Size and Carat Weight?

Choosing the best diamond based on size and carat weight involves considering several factors. First, understand that a larger carat weight does not always mean a bigger-looking diamond. The cut and shape of a diamond can influence its appearance and sparkle. Diamonds cut to ideal proportions often have greater brilliance and may visually appear larger than their actual size.

Consider your budget, as the price of a diamond increases exponentially with carat weight. Therefore, a diamond slightly below a full or half carat weight can still look the same size but at a significantly lower cost. Lastly, consider the setting and style of your engagement ring as it can affect the perceived size of the diamond.

Buying Diamonds from Accurate Precious Metals

Accurate Precious Metals is not a pawnshop. We are a reputable dealer located in Salem, Oregon. We offer fair and competitive rates for diamonds and gemstones based on their size, carat weight, and other factors. Even if you are not local, you can mail in your gold, silver, diamonds, or other jewelry, and we will provide you with an accurate and fair assessment. Contact us at 503-400-5608 or at

We believe in transparency and educating our customers so that they can make informed decisions about selling their precious metals or buying diamonds from us. Our team of diamond experts is always ready to assist you and answer any questions you may have about estimating carat weight from millimeters or choosing the perfect diamond for your needs.

  • Remember, carats are a unit of weight, while millimeters are a unit of size.
  • Two diamonds with the same carat weight can look different in size due to their cut and shape.
  • You can estimate the carat weight of a diamond from its dimensions in millimeters using a simple formula, but this provides an approximation, not the exact weight.
  • A diamond size chart is a helpful tool to estimate the weight of a diamond from its size in millimeters.
  • The cut of a diamond significantly influences its appearance and perceived size and weight.
  • Factors such as your budget, the diamond’s cut, and the ring’s setting should be considered when choosing a diamond based on its size and carat weight.
  • Accurate Precious Metals is a credible dealer and a great place to buy or sell diamonds and gemstones.

FAQs: Calculate Diamond Carat Weight & mm

Q: What does “mm” refer to in the Diamond Carat Weight Guide?

A: “mm” is the abbreviation for millimeters, which is a unit of measurement used to determine the size of a diamond or gemstone.

Q: What is a diamond carat?

A: A diamond carat is a unit of weight used to measure the size and mass of a diamond. One carat is equal to 200 milligrams.

Q: How are diamond carat and mm related?

A: Diamond carat and mm are related because the size of a diamond is determined by both carat weight and millimeter measurements. Generally, as carat weight increases, so does the mm size of a diamond.

Q: How do I convert mm to carat weight?

A: There is no direct conversion from millimeters to carat weight because other factors such as diamond shape and cut also play a role in determining carat weight. However, there are general size charts available that can give you an estimate of carat weight based on mm measurements.

Q: What is a round brilliant diamond?

A: A round brilliant diamond is a popular diamond cut known for its exceptional sparkle and fire. It features 58 facets and is commonly used in engagement rings.

Q: How can I estimate the weight of a round diamond?

A: You can estimate the weight of a round diamond by measuring its diameter in mm and using a conversion chart specific to round diamonds. This will give you a rough estimate of the carat weight.

Q: What other diamond shapes are commonly used in engagement rings?

A: Besides round brilliant diamonds, other popular diamond shapes used in engagement rings include princess cut, emerald cut, and radiant-cut diamonds.

Q: What are standard gem sizes for diamonds?

A: Standard gem sizes for diamonds vary, but some common sizes include 1 carat, half a carat, and quarter carat. These sizes are often used as benchmarks when buying diamonds.

Q: How do I calculate the carat weight of a diamond?

A: To calculate the carat weight of a diamond, you need to know its measurements (usually mm) and use a formula specific to the diamond shape. This calculation takes into account the depth, diameter, and other factors to determine the carat weight.

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