Weight and fineness, as the mints state them
A bullion coin is defined by two numbers: how much it weighs, and what fraction of that weight is the named metal. The platinum it contains is one multiplied by the other. This calculator stores the two numbers exactly as each issuing mint prints them on its own specification page and works the platinum out from them, rather than storing a rounded “1 oz” figure that could quietly disagree with the specification.
All four coins here are struck at the same fineness, 999.5 parts per thousand, often written .9995 or 99.95%. The United States Mint gives the American Platinum Eagle’s weight as 1.0005 troy ounces, 31.120 g. The Royal Canadian Mint gives the Platinum Maple Leaf as 31.11 g. The Royal Mint lists its 2018 one ounce platinum Britannia at 31.210 g. The Perth Mint gives its 2026 Platinum Kangaroo a minimum gross weight of 31.119 g, with a platinum content of 1.000 troy ounce.
Why the answers are not all exactly one ounce
Multiplying out the mints’ own figures gives slightly different results in the fourth decimal place. The Eagle works out at 31.104 g of platinum, a hair over one troy ounce, which is 31.1035 g. The Maple Leaf, from a weight printed to two decimal places, works out at 31.094 g, a hair under. The 2018 Britannia, at 31.210 g gross, works out at 31.194 g, about 0.003 troy ounce over. These differences are a small fraction of a gram, and they are shown as calculated rather than tidied to a round number.
The Perth Mint figure is a minimum, not a nominal weight, so the platinum worked out from it is a minimum too, and the calculator labels it that way. Where a mint states the platinum content directly — the US Mint and the Perth Mint both do — the site’s tests check that the worked-out figure agrees with it to within the precision of the printed weight.
Fractional coins, such as tenth- and quarter-ounce sizes, are not listed. Their specifications were not read from a mint page for this tool, and an estimate scaled down from the one-ounce coin is not the same thing as the mint’s own figure.
Gross weight is not platinum weight
Every coin weighs a little more than the platinum in it, because 999.5 fine leaves half a part per thousand for other metals. On a one-ounce coin that is about 0.016 g. It matters more for issues struck in lower finenesses, where the gap between what a coin weighs on a scale and the platinum it holds is much larger. For any coin not on this list the same arithmetic applies: weight multiplied by the fineness in parts per thousand, divided by 1,000. The platinum and palladium calculator on this site does that for any weight and fineness.
What melt value is, and what it is not
The value shown is melt value: the platinum content multiplied by the live platinum spot price. It is a measurement of the metal, in money. It is not what a dealer will charge for the coin or pay for it. Bullion coins generally change hands at a premium over the metal, and those premiums move with supply, demand, the dealer and the coin’s condition. Some years and special issues are collected, and a collector may pay considerably more than the metal for them.
This site does not recommend buying, holding or selling coins, and it does not name or rank dealers. The aim is narrower: to show exactly how much platinum a coin contains, so that any figure quoted for it can be compared with the metal underneath.
The price comes from the same live feed as every other value tool on the site. If the feed is down, the calculator shows no value at all rather than an old one, and the platinum weights remain correct, because they do not depend on the price.