Silver ounce: 31.1 grams, but coins rarely match

How much does a silver ounce weigh? 31.1 grams and a few tenths more

A silver ounce contains 31.10348 grams of pure silver. That's the exact figure. The problem is that almost no bullion coin weighs exactly that: it weighs a little more. And that's where confusion starts for those buying their first ounces, putting them on a two-decimal digital scale and seeing the needle fluctuate between 31.30 and 31.64 grams. Counterfeit or normal physics of mass minting? Almost always the latter.

How many grams does a silver ounce have and what the scale actually measures

The troy ounce equals 31.10348 grams, and that's the amount of fine silver, .999 purity, guaranteed by mints. The total weight of the piece is another matter: it includes the relief, the edge, and the minimal alloy adjustments of any industrial run. A mint can commit to each unit containing at least 31.1 grams of pure silver even if its gross weight varies by a few tenths. The distinction seems technical until you hold the coin and the scale doesn't match what you imagined.

The real weight of each coin: Koala, Kookaburra, and Philharmonic

Differences between models are perfectly measurable and documented by their manufacturers:

• Philharmonic (Austrian Mint): 31.30 g weight, .999 purity, 37 mm diameter, and 3.2 mm thickness.
• Koala (Australian Mint): 31.30 g, .999 purity, and 40.5 mm diameter.
• Kookaburra (Australian Mint): 31.64 g, almost half a gram above the fine content, with 40.6 mm diameter.

All three declare the same 31.10348 grams of silver. What changes is the metal accompanying the design. Some also claim that freshly minted ounces tend to weigh a few tenths more, and that a new piece below the fine content forces a scale check before doubting the coin.

Why the Kookaburra's thickness doesn't match the official one

Here the discrepancy is greater. Specifications from the Australian mint mention a maximum thickness of 4.00 mm and a maximum diameter of 40.60 mm. Measured with a caliper, reality is different: 3.00 mm thickness in all checked pieces, from 1990 to 2011, with the diameter spot on. The same happens with Koalas, which share declared dimensions and also come in at 3.00 mm. In cases like some 2009 Koalas bought from a German seller, measurements gave 40.45 mm diameter and 2.85 mm thickness, with weights of 31-something grams.

The nuance that resolves the contradiction: the mint publishes maximums, not exact measurements. It's not the usual certificate from a national mint, where diameter and thickness are detailed to the millimeter. That explains the perplexity, though it doesn't fully resolve it.

How to check the scale and when to really be suspicious

A 0 to 50 gram balance with two decimals, calibrated with a pharmacy standard weight, can still give different readings depending on the piece. Accuracy, precision, sensitivity, and reproducibility are four different things, and a home scale usually fails in one. Reasonable control combines weight, dimensions, and magnetism. As a field reference: above about 32 grams or below 30.5 grams, alarms should go off.

There's accumulated experience with Canadian Maple Leafs, where two columns of 25 coins from the same tube had different heights, almost one coin difference. The official response was that pieces can vary in size but each contains at least 31.1 grams of pure silver.

With those margins, it's foreseeable to keep finding tenths above and millimeters below. If after recalibrating the scale an ounce is still below 30.5 grams, then it's time to worry.