Diamond Carat Calculator — Weight & Price Estimator
Enter a diamond's carat weight to convert it to grams and milligrams, or estimate the carat weight of a round brilliant diamond from its diameter and depth. Add a price per carat (e.g. from a quote) to get a total price estimate.
Input method
ct
USD
One-carat
- 1
Carat to grams
1 × 0.2 = 0.2 - 2
Diamond weight
11 carat = 0.2 g = 200 mg (international standard).
How does this calculator work?
1 diamond carat = 0.2 grams (200 mg) — universally standardised since 1907. For a round brilliant cut, estimate carat weight from dimensions: ct ≈ diameter² × depth × 0.0061 (±5–10%). Multiply carats by price-per-carat for a total price estimate. Actual prices depend on cut, colour, and clarity.
Formula
How this is calculated
The metric carat (ct) is the unit of mass used for gemstones worldwide. Exactly 1 carat equals 200 milligrams (0.200 grams), a standard adopted by the General Conference on Weights and Measures in 1907 and universally applied by gem laboratories today. Converting between carats and grams is therefore a simple multiplication: grams = carats × 0.2.
When you have a loose round brilliant-cut diamond and want to estimate its carat weight without a scale, the industry uses a sizing formula: ct ≈ diameter² × depth × 0.0061, where diameter is the average girdle diameter in millimetres and depth is the total height from table to culet in millimetres. This is the simplified Leveridge approximation; results can vary by ±5–10% depending on the stone's proportions, cut style, and how girdle thickness is measured, so it is an estimate rather than a precise weight. A certified gem laboratory scale reading is always the authoritative weight.
Price per carat is a shorthand price quote used in the diamond trade. Multiply it by the carat weight to get a rough total price. Actual market prices depend heavily on the 4 Cs (cut, colour, clarity, and carat) and fluctuate with supply and demand — the price-per-carat field is an editable estimate and should not be taken as an exact market value.
Frequently asked questions
Exactly 0.200 grams (200 milligrams). This is an internationally standardised definition, not an approximation. So 0.5 ct = 0.10 g, 1 ct = 0.20 g, and 2 ct = 0.40 g.
The formula ct ≈ diameter² × depth × 0.0061 is a common industry approximation for round brilliant cuts. Accuracy is typically ±5–10%, depending on the stone's exact proportions, girdle thickness, and how the measurements are taken. For a precise weight, have the stone weighed on a certified gemological balance.
Not necessarily. A well-cut "ideal" round brilliant and a deep-cut stone of the same carat weight will appear visually different sizes because depth affects how much weight is hidden below the girdle. Cut quality, not just carat weight, determines face-up appearance. Two 1-carat diamonds from different cutters can differ in visible diameter by 0.5 mm or more.
Also known as
TG we-Calculate Editorial Team. (2026). Diamond Carat Calculator — Weight & Price Estimator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/diamond-carat-calculator
TG we-Calculate Editorial Team. "Diamond Carat Calculator — Weight & Price Estimator." TG we-Calculate. 2026. https://we-calculate.com/calculator/diamond-carat-calculator.
TG we-Calculate Editorial Team, "Diamond Carat Calculator — Weight & Price Estimator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/diamond-carat-calculator
@misc{wecalculate_diamond_carat_calculator, title = {Diamond Carat Calculator — Weight & Price Estimator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/diamond-carat-calculator}}, year = {2026}, note = {TG we-Calculate} }
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