Diamond Weight Converter

Diamond and gemstone weight uses the carat system.

Base relationships:

• 1 carat = 200 milligrams = 0.2 grams (exact, by international definition)
• 1 carat = 100 points
• 1 point = 2 milligrams = 0.002 grams

Other conversions:

• 1 carat = 0.00705 troy ounces
• 1 carat = 3.086 grains
• 5 carats = 1 gram (exact)

Common diamond sizes and weights:

Note: The gemstone carat (weight) is different from the gold karat (purity).

The single most useful thing to understand is that carat is weight, not size. Two one-carat diamonds can look noticeably different across the top, because a deep or poorly proportioned cut hides weight down in the stone where you can’t see it, while a well-cut stone of the same weight spreads wider and faces up larger. So “bigger carat” doesn’t always mean “looks bigger,” and cut quality is what bridges the gap.

Prices behave strangely around round numbers, too. There are “magic sizes,” half-carat, three-quarter, and especially one carat, where the price jumps sharply the moment you cross the threshold. A 0.95-carat stone can cost meaningfully less than a 1.00-carat one that looks identical to the eye, which is why careful buyers shop just under the round figures. The word itself comes from carob seeds, once used as a rough weight reference in ancient gem trading, long before a carat was standardized at exactly 200 milligrams.