Carats to Grams Converter
| Stone | Carats | Grams | Role |
|---|---|---|---|
| 0.5 ct | 0.1 | classic solitaire | |
| 0.75 ct | 0.15 | upgraded solitaire | |
| 1 ct | 0.2 | engagement default | |
| 2 ct | 0.4 | statement stone | |
| 5 ct | 1 | auction tier | |
| 10 ct | 2 | headline tier |
The cleanest conversion in jewelry: one metric carat is exactly 0.2 grams, fixed worldwide since 1907 - no approximation, no regional variant, five carats is a gram on the dot. Type a carat weight from a certificate and read the grams a jeweler's scale would show, or run it backwards from a scale reading to the carat line for a listing.
Do not confuse carat with karat, though - the gold one with a K. Karat measures gold purity (24K is pure), carat measures gemstone weight, and the two words share a etymology in the carob seed, which ancient traders used as balance weights because they grow remarkably uniform. The table carries the everyday stones, from the classic 0.5 ct solitaire to the 10 ct statements that make auction headlines.
How to use
- Type the carat weight from a certificate (ct, cts or the abbreviation CT) - grams appear instantly.
- Or run it backwards: a scale reading in grams divided by 0.2 is the carat weight for a listing.
- Compare stones with the table: 0.5 ct is the classic solitaire, 1 ct the engagement default, 5 ct and up are the auction statements.
Frequently asked questions
How many grams is 1 carat?
Exactly 0.2 grams - one fifth of a gram, set by the Fourth General Conference on Weights and Measures in 1907 and identical in every jewelry market since. Five carats is exactly one gram. The exactness is worth stating because so many jewelry units are fuzzy; this one is laboratory-grade, which is why certificates can state carat weight to the hundredth.
What is the difference between carat and karat?
Carat with a C weighs gemstones; karat with a K measures gold purity - 24 karat is pure gold, 18 karat is 75 percent gold by mass. Both words descend from the carob seed (keration in Greek), the ancient balance weight, and the spelling split happened centuries ago. A 18K gold ring with a 1 carat diamond: the K describes the band's alloy, the ct describes the stone sitting in it.
How big is a 1 carat diamond?
Carat measures mass, not size, so the answer depends on the cut - but a round brilliant 1 ct diamond runs about 6.4 to 6.5 mm across, roughly the diameter of a pencil eraser. Two diamonds of equal carat can look different sizes: a shallower cut spreads the same 0.2 grams wider, which is how some stones look bigger than their certificates claim.
Why do diamonds use carats while gold uses grams on the same receipt?
Tradition with regulation behind it: diamond pricing is built around the carat as a trading unit - prices jump at the magic marks (1.0 ct, 2.0 ct) in ways grams would hide - while gold is a commodity priced by mass, so grams and troy ounces rule. A receipt quotes both systems because both pricing structures are real. The converter is the bridge when comparing a 0.9 ct stone priced per carat against a 0.2-gram stone priced per gram.
Do pearls and colored stones use the same carat?
Yes - the metric carat (0.2 g) is the standard for pearls, diamonds and every colored gemstone alike. Pearls are often sold in carat for single stones and by mass for strands, and colored stones like emeralds and sapphires quote carat on certificates the same way diamonds do. What changes between stones is density: a 1 ct sapphire is visibly smaller than a 1 ct diamond, because sapphire packs more grams into the same volume.