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Convert Carat to Stone (ancient) (ct to st (ancient)) instantly with accurate, readable results.
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Carat (ct) — a metric unit of mass for gemstones
It is defined as exactly 200 milligrams, or one fifth of a gram. Used worldwide for measuring diamonds, gemstones, pearls, and other jewels; it should not be confused with karat, which measures gold purity.
- Symbol: ct
- System: Non-SI metric unit for mass; used with SI
- Exact relations: 1 ct = 200 mg = 0.2 g = 0.0002 kg
- Imperial equivalents (derived from 1 lb = 0.45359237 kg exactly): 1 ct ≈ 0.00705479 oz ≈ 0.000440925 lb
- Typical examples: a small diamond ~0.25 ct; an engagement-ring diamond ~1 ct; large gemstones may be several ct.
Stone (ancient) — a variable historical unit of mass
It was not a single fixed unit; in ancient and medieval use, a “stone” could mean a locally chosen trade weight, often varying by region, period, and commodity. Used historically for weighing goods such as wool, grain, meat, and other trade commodities, and for stone weights used as practical measuring standards.
- Symbol: stone, st
- System: Historical unit for mass; not a fixed SI or modern imperial standard in ancient use
- Common historical range: about 4 to 32 lb ≈ 1.814 to 14.515 kg, depending on context
- Modern reference point: the later British imperial stone is exactly 14 lb = 6.35029318 kg
- Typical examples: trade stones could be used for wool, grain, or livestock products; a “stone” in one market might differ from a “stone” in another; historical records should be interpreted by period and location.