Every figure below uses the same constants as the converter: 1 carat = 200 mg, 1 Kachi Ratti = 120 mg, 1 Pakki Ratti = 180 mg.
Carat and ratti — two systems, one stone
The carat is the international unit of gemstone weight: exactly 200 milligrams, standardised worldwide and used on every laboratory certificate. The ratti is the traditional Indian unit, and it is the measure most astrologers use when they recommend a gemstone — "a 5-ratti Yellow Sapphire", for instance.
The two coexist on almost every Indian gemstone purchase: the certificate states carats, the recommendation states rattis. What makes the bridge between them worth getting right is that "ratti" itself has two conventions — Kachi Ratti at 120 mg and Pakki Ratti at 180 mg. Select the one your recommendation uses before comparing weights.
Kachi Ratti — 120 mg
One Kachi Ratti is 120 milligrams, which is 0.120 gram and 0.60 carat. To go the other way, divide milligrams by 120, grams by 0.120 or carats by 0.60.
So a 5-Kachi-Ratti stone weighs 600 mg — 0.600 gram, or 3.00 carats. A 1-gram stone is 8.3333 Kachi Ratti, and a 5-carat stone is likewise 8.3333 Kachi Ratti.
Pakki Ratti — 180 mg
One Pakki Ratti is 180 milligrams, which is 0.180 gram and 0.90 carat. Reversing it, divide milligrams by 180, grams by 0.180 or carats by 0.90.
A 5-Pakki-Ratti stone therefore weighs 900 mg — 0.900 gram, or 4.50 carats. A 1-gram stone is 5.5556 Pakki Ratti, and a 5-carat stone is likewise 5.5556 Pakki Ratti.
Carat, gram and milligram
These three never move with the ratti standard you select. One carat is exactly 0.2 gram and 200 milligrams, so dividing a carat weight by 5 gives grams; one gram is exactly 5 carats and 1000 milligrams.
Because those definitions are exact, the conversions carry no rounding at all — they are the same in every laboratory and every market in the world. Only the ratti column changes when you switch between Kachi and Pakki.
