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1/20 oz Gold Bars

The gram comes from water.

The gram was laid down in Paris, in the law of 18 Germinal, Year III, which by our calendar was 7 April 1795. Article 5 reads:

“Gramme, le poids absolu d’un volume d’eau pure égal au cube de la centième partie du mètre, et à la température de la glace fondante.”

Law of 18 Germinal an III (7 April 1795), Article 5

This means the weight of pure water in a cube with edges of one centimetre, at the temperature of melting ice. The kilogram was merely its multiple: Article 7 calls it the weight of a thousand grams.

Both weigh one gram.
  1. Water10 mm edge
  2. Gold15 × 8.7 mm

Both at the same scale. The cube shows the gram as defined by the law of 1795. Beside it is a bar of 1 gram by Heimerle + Meule, with the dimensions given by the maker.

Twenty drops of water from a standard dropper together weigh about one gram.

In Germany, the gram has applied since 1 January 1872, as laid down in the Maß‑ und Gewichtsordnung of 17 August 1868, the weights and measures act of the North German Confederation. Article 6 states: “The kilogram is divided into 1,000 grams”. And: “Half a kilogram is called the pound.”

From 1889, the measure was tied to a cylinder of platinum and iridium, the International Prototype of the Kilogram near Paris. The first General Conference on Weights and Measures resolved: “This prototype shall henceforth be considered as the unit of mass.” Germany’s copy, number 52, is kept under two glass bell jars at the Physikalisch‑Technische Bundesanstalt (PTB), the national metrology institute, in Braunschweig.

According to the PTB, the last comparisons showed that the difference between the prototype and its copies had grown to 50 micrograms, “about the same mass as the wing of a fly”. Since 20 May 2019, the kilogram has been tied to a constant of nature, the Planck constant.

Cylindrical brass weight with a knob on top
The first standard kilogram of the Netherlands, made in Paris in 1798. The plaque on its case reads: “Kilogramme conforme a la loi du 18 Germinal an 3 …”. When it was reweighed in 1847, it was 16 milligrams lighter than the new standard. Rijksmuseum Amsterdam, public domain.

Where gold is not weighed in grams.

The gram is not the measure for gold everywhere. In Vietnam, people count in lượng and chỉ. A government decree laid this down in 2012: one lượng is 37.5 grams, one chỉ 3.75 grams, both only for weighing gold and silver.

In Hong Kong, the Chinese Gold and Silver Exchange Society trades gold in taels. There, one tael is 37.429 grams.

The troy ounce, in which many coins and bars are weighed, is also built from a smaller measure, the grain: 480 grains make one troy ounce, and one grain weighs 64.79891 milligrams. This is set out in Handbook 44 of NIST, the U.S. National Institute of Standards and Technology.

Five measures for gold, in grams
  1. 1 gram Law of 17951 g
  2. 1 chỉ Vietnam3.75 g
  3. 1 troy oz 480 grains31.10 g
  4. 1 tael Hong Kong37.43 g
  5. 1 lượng Vietnam37.5 g

The values are given by Decree 86/2012 of the Vietnamese government, the Chinese Gold and Silver Exchange Society in Hong Kong and NIST. The troy ounce and the tael are rounded to two decimal places.

Copper weight shaped like a violin, with Chinese characters incised at the top
Chinese tael weight from the wreck of the East Indiaman “’t Vliegend Hart”, made between 1700 and 1735. Such weights were used to weigh gold and other valuables, according to the museum. Rijksmuseum Amsterdam, public domain.

Three quarters of a tonne of rock for one gram.

Gold that comes out of the ground today is usually invisible, locked away in the rock. In the second quarter of 2022, the ore processed by gold mines worldwide contained an average of 1.29 grams of gold per tonne. Metals Focus reports this in an article for the World Gold Council.

By calculation, one gram of gold is therefore contained in about 775 kilograms of ore, just over three quarters of a tonne.

One gram of gold in about 775 kilograms of ore
  • one tonne
  • about 775 kg of ore
  • 1 g gold

Diagram: the square stands for one tonne. Only the golden dot is not to scale. At the same scale, it would be smaller than a pixel.

Ordinary rock holds far less gold still. On average, the Earth’s crust contains 0.004 grams per tonne, according to the U.S. Geological Survey. By calculation, that would be 250 tonnes for one gram.

On the Witwatersrand in South Africa, about 5.87 billion tonnes of rock were mined and milled from 1886 to 2005. On average, they yielded 8.07 grams of gold per tonne.

Close‑up of gold ore: pale and grey pebbles in dark rock
Gold ore from the Witwatersrand. U.S. Geological Survey, public domain.

One gram of Rhine gold.

The Rhine carries gold too, in tiny flakes. The Federal Institute for Geosciences and Natural Resources (BGR) writes:

“In the Rhine, placer gold occurs almost exclusively in the form of the finest flakes up to 0.3 mm in diameter and 0.003‑0.005 mg in weight.”

Federal Institute for Geosciences and Natural Resources, Commodity Top News No. 30, 2009

By calculation, one gram of Rhine gold is therefore 200,000 to about 330,000 flakes.

A flake next to the same bar of 1 gram
  1. Flake0.3 mm
  2. 1 g bar15 × 8.7 mm

Both at the same scale. The fine circle only shows where the flake lies. The maximum size of the flakes is given by the Federal Institute for Geosciences and Natural Resources, the dimensions of the bar by Heimerle + Meule.

In 1960, a gravel works near Bruchhausen, south of Karlsruhe, separated 21.3 grams of gold from 50,000 cubic metres of gravel. By calculation, that makes about 2,350 cubic metres of gravel for one gram.

The gold panners had a rule of thumb: for panning to be worthwhile, a shovelful of sand had to contain 10 to 20 flakes near Strasbourg and at least 40 to 50 near Mannheim. Downstream, the flakes become ever finer.

In 1874, the Karlsruhe Mint received its last Rhine gold: 89.8 grams.

From strip to bar.

How fine gold becomes a small minted bar is described step by step in the reference work Gold Bars Worldwide, based on information from the Perth Mint in Australia. For this, the gold is rolled into a strip.

Before the blanking press runs, individual trial blanks are cut from the strip with a hand press and weighed. If one is too heavy, the strip goes through the rolling mill once more.

Then a press punches the blanks out of the strip, and every single one is weighed. Blanks that are too light or clearly too heavy go back into the melt, as does the webbing left over from the strip.

The blank is struck between two dies, while a ring, the collar, holds its shape. Sometimes it takes more than one strike.

Four steps to a bar
  1. Strip
  2. Blank
  3. Balance
  4. Dies

15,000bars of standard quality, at most, can be struck with one die. After about 5,000, it is usually repolished.

Diagram based on information from the Perth Mint.

Old black‑and‑white photograph: an empty hall with long tables, a small balance at every place, machines at the back
The coin adjusting room of the U.S. Mint in San Francisco: a balance at every place and, at the back, machines for counting the coins. Photograph taken between about 1870 and 1930. U.S. National Archives, public domain.
View 1 g gold bars
Sources: Law of 18 Germinal an III (7 April 1795), Articles 5 and 7, after the Digithèque MJP of the University of Perpignan; Maaß‑ und Gewichtsordnung für den Norddeutschen Bund of 17 August 1868, Articles 6 and 21 (Bundesgesetzblatt des Norddeutschen Bundes 1868, p. 473; the quotations are translated from the German); Physikalisch‑Technische Bundesanstalt (Das Kilogramm; Das Kilogramm, die Einheit der Masse; the quotation is translated from the German); Bureau International des Poids et Mesures (1st and 26th General Conference on Weights and Measures; the declaration of 1889 is quoted in the BIPM’s English wording); European Pharmacopoeia, 2.1.1 Droppers, after the 2024 draft of the Austrian Pharmacopoeia; Decree 86/2012/NĐ‑CP of the Government of Vietnam, Annex IV; Chinese Gold & Silver Exchange Society (Hong Kong); NIST Handbook 44, 2026 edition, Appendix C; World Gold Council (Gold Focus, 30 September 2022, after Metals Focus); U.S. Geological Survey (Mineral Commodity Profiles: Gold, 2005); M. Handley, Journal of the Southern African Institute of Mining and Metallurgy 123 (2023); Federal Institute for Geosciences and Natural Resources, BGR (Goldgewinnung in Deutschland, 2009; the quotation is translated from the German); Gold Bars Worldwide, based on information from the Perth Mint (How minted gold bars are manufactured, 2014); Heraeus, Argor‑Heraeus, Umicore, Valcambi and Heimerle + Meule (dimensions of the 1 g bars). Images: first standard kilogram of the Netherlands, 1798, and tael weight from the wreck of the “’t Vliegend Hart” (both Rijksmuseum Amsterdam, public domain), gold ore from the Witwatersrand (U.S. Geological Survey, public domain), coin adjusting room of the U.S. Mint in San Francisco (U.S. National Archives, public domain).
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