Diamond Carat Size Calculator
Estimate the approximate dimensions of a diamond in millimeters based on its carat weight and shape. See the estimated length, width, depth, face-up area, and length-to-width ratio.
A 1.00 ct round diamond is approximately 6.50 mm wide.
How to Use the Diamond Carat Size Calculator
Enter the diamond’s carat weight, select its shape, and click Calculate Diamond Size.
The calculator estimates the diamond’s:
- Length in millimeters
- Width in millimeters
- Depth in millimeters
- Face-up area
- Length-to-width ratio
Use these measurements to get a general idea of how a diamond of a particular carat weight may look from the top.
What Does Diamond Carat Size Mean?
Carat measures weight, not physical dimensions. One metric carat equals 0.20 grams. Two diamonds with the same carat weight can have different measurements because their shapes and proportions can differ.
For example, a 1-carat round diamond and a 1-carat oval diamond will not normally have the same length and width.
Why Do Diamond Dimensions Vary by Shape?
Different diamond shapes use different proportions and cutting styles. A round diamond is measured primarily by its diameter, while fancy shapes such as oval, pear, emerald, and marquise are generally described using length × width × depth.
That is why this calculator asks you to select the diamond shape rather than converting carat weight directly into one universal measurement.
What Is Length-to-Width Ratio?
The length-to-width ratio compares a diamond’s length with its width:
Length-to-Width Ratio = Length ÷ Width
A ratio close to 1.00 produces a more square or rounded outline, while a higher ratio produces a more elongated appearance. This measurement is particularly useful when comparing fancy shapes such as oval, pear, and marquise diamonds.
Are These Diamond Measurements Exact?
No. The results are estimated dimensions, not measurements of a specific diamond.
Actual dimensions can vary because diamonds of the same carat weight can have different proportions, depth, girdle thickness, and cutting styles. GIA notes that diamond proportions can vary considerably and influence the stone’s face-up appearance.
If you are buying a specific diamond, use the length, width, and depth shown on its grading report for its actual measurements. GIA reports these measurements in millimeters.
Diamond Carat Size vs. Diamond Weight
It is easy to confuse carat weight with visible diamond size.
A larger carat weight does not automatically mean a diamond will look proportionally larger from the top. The way the diamond is cut and how its weight is distributed can affect its face-up dimensions.
For comparing how large a diamond may appear, looking at millimeter measurements and face-up area can therefore be more useful than considering carat weight alone.
Disclaimer
This calculator provides approximate diamond dimensions for informational purposes only. Actual measurements vary between individual diamonds because of differences in shape, proportions, depth, girdle, and cutting style.
For an exact diamond, always refer to the measurements on its grading report.
That’s all I’d put on this page. No FAQ, no long explanation of the 4Cs, and no generic diamond-buying article. The calculator is the main feature, and these sections explain exactly what users need to understand its results.