Gross weight, fineness and fine weight
A gold bar is stamped with two numbers that matter: its weight and its fineness. The weight is the gross weight — everything in the bar. The fineness is the share of that weight which is pure gold, in parts per thousand. Multiply one by the other and you have the fine weight, the amount of pure gold the stamp claims. A 1 kilogram bar stamped 999.9 contains 999.9 grams of gold; the other 0.1 gram is whatever else the refined metal contains.
That is the whole calculation, and nothing in it is estimated. The calculator converts the weight from grams, troy ounces, kilograms or tola using the exact definitions — a troy ounce is 31.1034768 grams, a tola three eighths of a troy ounce — and gives the fine gold in grams, troy ounces and kilograms.
Why fine weight is the number that counts
Gold is quoted by the troy ounce of pure gold, so the fine weight is what any spot-price comparison has to start from. For bars stamped 999.9 the difference between gross and fine weight is tiny, but it is not zero, and for a large bar at a lower fineness it is not small. A bar of 400 troy ounces at 995.0 fine contains 398 fine ounces, two ounces short of its gross weight.
Fine weight is also how the wholesale market counts bars. The London Good Delivery specification is written in fine troy ounces, not gross, for exactly this reason.
The London Good Delivery bar
The LBMA, which runs the London bullion market, publishes the specification for the large gold bars that trade there. A Good Delivery gold bar must contain a minimum of 350 and a maximum of 430 fine troy ounces of gold — about 10.9 to 13.4 kilograms — at a minimum fineness of 995.0 parts per thousand. Its gross weight is stated in troy ounces in multiples of 0.025, rounded down.
That is why wholesale bars are usually described as “about 400 ounces” rather than an exact round figure: each bar is weighed and stamped individually. The calculator shows whether a bar’s numbers fall inside the Good Delivery range, but that is a comparison of numbers only. A Good Delivery bar is also defined by its refiner being on the LBMA’s list, its shape and its marks, none of which a calculator can check.
Small bars
Bars of 1 gram to 1 kilogram are made to their refiners’ own specifications, not to Good Delivery, and carry their own weight and fineness stamps. Check whether a stated weight is gross or fine before entering it: this calculator expects the gross weight. The size presets on this page are the nominal weights those bars are labelled with; enter the exact weight from the stamp or certificate if it differs.
The tola bar, common in South Asia and the Gulf, is a multiple of the tola, three eighths of a troy ounce. A ten tola bar is 116.64 grams gross.
What a stamp cannot tell you
The calculation takes the stamp at its word. Whether a bar actually contains what it claims is a question for an assay: a fire assay, or non-destructive tests such as X-ray fluorescence and ultrasound, which measure different things and have different limits. Counterfeit bars with a tungsten core exist because tungsten’s density is close to gold’s, so weight and size alone may not reveal them; the metal density comparison page sets out the published figures.
Fine weight is also not a price. Bars change hands at a price agreed between buyer and seller, which can sit above or below the value of the fine gold at spot. To see the melt value of a fine weight at today’s price, enter it in the gold price per gram tool. This page measures the gold and stops there.