Carat vs Ratti: How to Calculate the Right Gemstone Weight

A customer asks for a 5 ratti Pukhraj. The seller quotes for 5 carat. The difference is nearly 10 percent by weight and a great deal more in price - and both parties think they agreed.

The two units

Carat is the international trade standard. One carat is exactly 200 milligrams, or 0.2 grams. Every laboratory report in the world states weight in carats.

Ratti is the traditional South Asian unit, historically based on the seed of the Abrus precatorius plant. Because it began as a natural object, its value varied regionally. The convention in general use today is:

• 1 ratti = 0.91 carat (approximately)
• 1 carat = 1.0989 ratti (approximately)

So a 5 ratti stone weighs about 4.55 carat, and a 5 carat stone is about 5.49 ratti. Always confirm which unit a quoted weight is in, and ask for the carat weight from the certificate as the definitive figure.

Some sellers quote in ratti because it makes the number look bigger. That is not dishonest in itself - but you should always convert to carat before comparing prices.

The body weight rule

The most widely used traditional guideline sizes a stone to the wearer:

Gemstone weight in ratti = body weight in kilograms ÷ 10

A 70 kg person therefore uses roughly a 7 ratti stone. A 55 kg person, roughly 5.5 ratti.

Our carat to ratti calculator does the arithmetic in both directions, including the body-weight suggestion.

Where the rule needs adjusting

The formula is a starting point, and several factors move the answer.

• Stone density. Coral and pearl are light for their volume, so higher ratti figures are conventional - 6 to 9 ratti for coral is normal.
• Diamond. Never sized by the body-weight rule. Venus's stone is prescribed by carat, usually between 0.5 and 2.
• Powerful stones. For Neelam, Gomed and Lehsunia, many astrologers deliberately start below the calculated figure and increase later if the trial goes well.
• Chart strength. A severely weak planet may warrant more; a moderately weak one, less.
• Practicality. A 9 ratti ring is a large object. If it will not be worn, it does nothing.

Minimum effective weight

Most practitioners hold that below roughly 3 ratti a stone is decorative rather than remedial. If budget forces a choice between a small stone of top quality and a properly sized stone of good quality, the conventional advice is to take the correct size and accept slightly lower clarity - with the exception of Neelam, where quality is not something to compromise.

Checking what you actually received

1. Read the carat weight on the lab certificate - not the seller's description.
2. Convert to ratti by multiplying by 1.0989.
3. Compare against what you ordered. Small variance is normal; a full ratti is not.
4. If the stone is already set, ask for the pre-setting certificate. Weighing a mounted stone accurately is not possible.

Every certified stone we ship states carat weight on its report, verifiable on the certificate validation page. Browse certified gemstones.