Carat. The unit of weight used for diamonds — one carat equals 0.2 grams or 200 milligrams. Carat is a measure of weight, not size. Pricing rises sharply at round numbers (1.00, 1.50, 2.00 ct), so a 0.99 ct stone is meaningfully cheaper than a 1.00 ct stone of equal quality.
Diamond price per carat does not scale linearly. A 2 ct stone typically costs four to five times what a 1 ct stone of equal quality costs, because larger rough is exponentially rarer.
The same logic applies on resale. Crossing the 1 ct or 2 ct threshold can lift an offer by 20% or more, even though the visual difference between 0.98 and 1.02 ct is invisible without a scale.
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