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Carats to Grams Converter
↔ Convert g to ct instead

Common Conversions

ct g
0.01 0.002
0.1 0.02
0.25 0.05
0.5 0.1
1 0.2
2 0.4
5 1
10 2
25 5
50 10
100 20
1000 200

Why this conversion matters in chemistry

The carat belongs mostly to gemology, not chemistry — but crystal-specimen work and mineralogical research do cross over occasionally, and any analytical instrument that weighs a sample will report in grams rather than carats. The conversion is clean: 1 ct = 0.2 g exactly, fixed in 1907 to replace the historically variable carob-seed weight. A 2.5 ct sapphire is 0.5 g. There's nothing chemically interesting about the arithmetic, but if a mass keeps arriving in carats and your instrument wants grams, this is the step that bridges them.

Formula

g = ct × 0.2

Worked Examples

1 ct = 0.2 g

The base conversion — exactly 200 milligrams, pinned by international agreement.

5 ct = 1 g

A clean round anchor. Five carats is a gram; useful for sanity-checking mental conversions.

0.5 ct = 0.1 g

A half-carat specimen. Small enough to handle on a microbalance.

100 ct = 20 g

A large crystal specimen — say, a research-grade mineralogy sample.

Frequently Asked Questions

How do I convert carats to grams?
Multiply by 0.2. So 5 ct becomes 1 g, and 0.25 ct becomes 0.05 g. The factor is exact — no rounding needed. The conversion shows up most often in mineralogical specimen logging and gemological testing, where specimens arrive catalogued in carats but every analytical instrument downstream wants a gram reading.
Why is a carat exactly 0.2 g?
Historical convenience, crystallized into an international standard in 1907. The unit traces to ancient Mediterranean trade, where small seeds — traditionally carob, though the actual history is disputed — served as counterweights for weighing gemstones. The 1907 metric-carat definition pinned it to 200 mg exactly so the unit could play nicely with SI.
Is this the same as the karat that measures gold purity?
No — they're completely different units that happen to sound alike. Carat (ct) is a mass. Karat (K) is a purity fraction, parts out of 24, so 24K is pure gold and 18K is 75% gold. Worth keeping straight because the spellings are so close.