Gold weight and purity converter

Gold can be described in grams, troy ounces or traditional units such as the tola, depending on who is talking. This page converts between them, works out how much fine gold an item contains for its carat, and explains why “carat” means two different things.

Weight

Fine gold by carat

Carat purity is counted in 24ths: 24 carat is all gold by this count, 18 carat is 18 parts gold in 24 (75 percent) and 12 carat is half. In practice, NIST notes that an item marked 24 k is 99.9 percent gold, so pure gold in trade is not quite 100 percent. Source: National Institute of Standards and Technology, Office of Weights and Measures, Conversion Factors for Precious Metal Sales (rev. March 2015), checked 26 October 2026. BIS asks for the bill to state purity in carat and fineness; where the stated fineness differs from the simple carat ÷ 24 share, go by the stated fineness.

Gemstone carats

Carat means two different things

The carat on a gold hallmark is a measure of purity: how many of 24 parts are gold. The carat used for diamonds and other gemstones is a unit of weight: one metric carat is 0.2 gram, or 200 milligrams. NIST notes that it began as the weight of a carob seed and was later standardised at 0.2 gram. Source: National Institute of Standards and Technology (NIST), Precious metals conversion, checked 26 October 2026. A 22 carat ring and a 1 carat stone have nothing in common except the word.

What a BIS hallmark tells you

• The Bureau of Indian Standards permits hallmarking of 14, 18, 20, 22, 23 and 24 carat gold jewellery and artefacts, and says the bill should state the item’s purity in carat and fineness. Source: Bureau of Indian Standards, Hallmarking FAQ (general), checked 26 October 2026.
• You can check the HUID number on hallmarked jewellery before buying, with the “Verify HUID” feature in the BIS CARE app. BIS also says a hallmark stays valid for the life of the jewellery. Source: Bureau of Indian Standards, Hallmarking FAQ under the mandatory system: consumers, checked 26 October 2026.
• If you doubt the purity, you can have the item tested, for a fee, at a BIS-recognised assaying and hallmarking centre. If hallmarked jewellery is found to be less pure than marked, BIS states that the buyer is entitled to compensation of two times the amount of the difference for the shortfall in purity, plus the testing charges. Source: Bureau of Indian Standards, Hallmarking: consumer protection, checked 26 October 2026.

Tola and ratti

The tola was an official Indian weight. The Standards of Weight Act, 1939 defined the standard tola as a weight of 180 grains; we read that definition as reproduced in the schedule of Assam’s 1955 Act adopting those standard weights. Source: Assam Legislature (text on India Code), The Assam Adoption of Standard Weights Act, 1955 (Assam Act IX of 1955), First Schedule, checked 26 October 2026. When India moved to metric units, the Standards of Weights and Measures Act, 1956 set the conversion rate at 1 tola = 0.0116638 kilogram, that is 11.6638 g, and the converter uses that figure. The two agree: 180 grains of 64.798 91 mg each make 11.663 803 8 g. Source: Parliament of India (text on India Code), The Standards of Weights and Measures Act, 1956 (Act 89 of 1956), First Schedule, checked 26 October 2026.

India Code lists the 1956 Act as repealed in 1976, so treat the tola as a historical unit with a well-defined value, not as a unit in current law. When a figure matters, ask for the weight in grams on the bill.

The ratti (rati) is a smaller traditional weight. The Assam schedule lists one rati as 1/96 of a tola, which works out to about 0.1215 g. Source: Assam Legislature (text on India Code), The Assam Adoption of Standard Weights Act, 1955 (Assam Act IX of 1955), First Schedule, checked 26 October 2026. That is one state’s historical schedule, and we did not find a national definition. Maharashtra’s Sangli District Gazetteer lists the ratti among the old units for weighing precious stones, and notes that the old weights and measures “differed from place to place and also sometimes for each commodity at the same place”. Source: Gazetteers Department, Government of Maharashtra, Sangli District Gazetteer (1969; e-book edition 2006), Banking, Trade and Commerce: Weights and Measures, checked 26 October 2026. When we checked on 26 October 2026, this government site’s security certificate had expired (25 February 2026), so your browser may warn you before opening it. So the converter does not assume any ratti value. If you are quoted a weight in ratti, ask the seller for the grams they count per ratti and enter that figure above.

Gram, troy ounce, pennyweight, grain and tola

A troy ounce is 20 pennyweights or 480 grains. Source: National Institute of Standards and Technology, Office of Weights and Measures, Conversion Factors for Precious Metal Sales (rev. March 2015), checked 26 October 2026. The grain is exactly 64.798 91 milligrams. Source: National Institute of Standards and Technology (NIST), NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically (SP 811), checked 26 October 2026.

Values checked 26 October 2026. Next review due 26 October 2027.

This page is past its review date (26 October 2027). Official values can change, so check the linked sources before relying on these figures.