Two numbers on the bar, one answer
A silver bar is stamped with its weight and its fineness. The fineness is the share of that weight which is silver, in parts per thousand: 999 means 999 parts in every 1,000 are silver, and 999.9 means 9,999 parts in 10,000. The pure silver in the bar is the weight multiplied by the fineness and divided by 1,000. Nothing in that is estimated. A 1 kg bar at 999 contains 999 g of silver, which is 32.119 troy ounces.
The gross weight can be entered in grams, kilograms, troy ounces or tola, the units silver bars are commonly stamped in. A troy ounce is exactly 31.1034768 g, and a tola is exactly three-eighths of a troy ounce. The kitchen ounce of 28.35 g is not used for precious metals and is not offered here, because confusing the two understates a bar by almost a tenth.
The London Good Delivery silver bar
The large bar traded between banks and refiners in the London market is the Good Delivery bar, and the London Bullion Market Association publishes its specification. A Good Delivery silver bar must contain at least 750 and at most 1,100 troy ounces of silver, about 23 to 34 kg, and its fineness must be at least 999.0 parts per thousand. Its gross weight is stated in troy ounces in multiples of 0.10, always rounded down. The LBMA asks refiners to aim for 900 to 1,050 ounces; in the trade they are often called “thousand-ounce bars”.
The silver limits apply to the fine silver content, not to the bar’s gross weight. The calculator compares the right number: a bar weighing 750.5 ounces gross at 999.0 fine holds only 749.75 ounces of silver, so it falls below the minimum even though its gross weight is above it. The marks the LBMA requires on each bar are its serial number, the refiner’s assay stamp, its fineness and its year of manufacture.
The comparison on this page is with numbers only. A Good Delivery bar is also defined by being produced by a refiner on the LBMA’s list, and by its shape, surface and marks, none of which a calculator can check. Small retail bars are made to their refiners’ own specifications, and are not expected to meet the wholesale one at all.
What the stamp proves, and what it does not
The figure on this page is what the stamp states, multiplied out. Whether the metal in the bar matches its stamp is a question for an assay. A refiner’s mark is the refiner’s claim; the bar’s weight on an accurate scale is the first independent check anyone can make, and a weight well below the stamp is a reason to look further.
Fine weight is a measurement, not a price. Bars change hands at prices agreed between buyer and seller, which can sit above or below the value of the fine silver at spot. For the value of the silver at today’s price, enter the bar’s gross weight and its fineness into the silver value calculator.