Bullion Coin Authenticity Test — Check Weight, Size and Thickness
Recommended Equipment
€30–80 · 0.01 g resolution as a floor, 0.001 g preferably
€15–40 · ±0.02 mm, handles both diameter and depth
€5–10 · for the slide test that exposes ferrous cores
Note: Treat this as a physical screening rather than a certificate. Instrumental analysis — XRF or ultrasound — reaches conclusions that measurement alone cannot, and it is worth arranging for anything of substantial value. It is also worth knowing that Ireland operates one of the oldest hallmarking regimes in Europe: articles of precious metal offered for sale here must be assayed and marked by the Assay Office at Dublin Castle, which has been doing the job since 1637. Legal-tender coinage falls outside that requirement, so a bullion coin will never carry an Irish hallmark.
Just the weight, measured against each mint's stated tolerance.
Diameter and depth examined in their own right.
What the raw metal is worth in bars, coins, alloys and old jewellery.
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Getting something out of what you see and read?
We put our whole heart into keeping preciousmetalprices.com fast, tidy and free — no paywalls, no clutter, just facts and live prices you can trust. If it’s any help to you, the nicest way to say thanks is to pass it along. Every share helps another investor find us and keeps the whole project ticking over. 💛
How to Tell a Genuine Coin from a Convincing Fake
The higher gold climbs, the more attractive forgery becomes — and gold has rarely been higher. There is a consolation in that, though, and it is a substantial one: the laws of physics cannot be counterfeited. Mass, breadth and depth are bound together by the density of the metal. Get all three to agree simultaneously and there is scarcely any material left that could be hiding underneath.
The five checks and the order to run them in
Assess the strike, the finer details, the milling and the shade of the metal.
A 0.01 g scale, read against the published figure.
Caliper across the coin, then through it.
An N52 magnet released onto the tilted surface.
A tap on the rim: the genuine article sustains the note.
Everything you need for less than €100
Modest outlay, considerable coverage: these three instruments between them catch upwards of 95 % of counterfeits.
Why Density Gives Counterfeiters Away
No two metals pack the same mass into the same space. Substitute the material while keeping the weight, and the coin is forced to change shape — which is precisely what a caliper is for.
Worked Example: Copper in Place of Gold
Suppose a forger reaches for copper. The genuine coin fits 31.103 g of gold into some 1.61 cm³; copper, at 8.96 g/cm³, would need about 3.47 cm³ for the same mass — 2.15 times the volume. Something has to give, and it is the thickness: roughly 4.3 mm instead of 2.8 mm. No caliper on earth would miss that.
Tungsten — the serious problem
Only one metal genuinely troubles this approach. Tungsten measures 19.25 g/cm³, a mere 0.36 % away from gold, which allows a well-made fake to satisfy both the scale and the caliper.
Published Specifications for the Main Bullion Coins
Below are the published specifications for the ten 1 oz bullion coins that trade in the greatest volume worldwide. The three quantities the calculator above asks for — weight, diameter, thickness — appear in their own columns. So does the weight tolerance, the deviation each mint accepts as normal production variation; a coin sitting inside that band has nothing to answer for.
| Coin | Fineness | Weight | Tolerance | Diameter | Thickness |
|---|---|---|---|---|---|
|
🇨🇦
Maple Leaf
|
999.9‰ | 31.103 g | ±0.030 g | 30.00 mm | 2.87 mm |
|
🇦🇹
Vienna Philharmonic
|
999.9‰ | 31.103 g | ±0.030 g | 37.00 mm | 2.00 mm |
|
🇿🇦
Krugerrand
|
916.7‰ | 33.930 g | ±0.070 g | 32.77 mm | 2.84 mm |
|
🇺🇸
American Eagle
|
916.7‰ | 33.931 g | ±0.060 g | 32.70 mm | 2.87 mm |
|
🇺🇸
American Buffalo
|
999.9‰ | 31.108 g | ±0.030 g | 32.70 mm | 2.95 mm |
|
🇬🇧
Britannia
|
999.9‰ | 31.103 g | ±0.030 g | 32.69 mm | 2.55 mm |
|
🇦🇺
Kangaroo (Nugget)
|
999.9‰ | 31.103 g | ±0.030 g | 32.10 mm | 2.65 mm |
|
🇨🇳
China Panda
|
999.0‰ | 30.000 g | ±0.030 g | 32.00 mm | 2.60 mm |
|
🇬🇧
Sovereign
|
916.7‰ | 7.988 g | ±0.016 g | 22.05 mm | 1.52 mm |
|
🇲🇽
Libertad
|
999.0‰ | 31.103 g | ±0.030 g | 34.50 mm | 2.69 mm |
All values relate to the 1 oz format, the Sovereign excepted at 7.988 g, and the tolerances are those published by the respective mints. Should you want the weight assessed on its own with a traffic-light result, the Weight Checker handles that.
Getting Accurate Readings from a Caliper
The scale comes first, the caliper immediately after. For €15 to €40 you acquire ±0.02 mm of certainty, which is finer than any deviation that would matter in practice.
Bring the jaws together and hit ZERO. The faces need to be clean and completely dry beforehand.
Hold the coin in the outer jaws with the line running through the centre. Rotate 60°, measure again, repeat, then take the mean of three.
Switch to the depth faces and work in the middle of the coin, never against the rim. Three readings, averaged.
Mistakes That Ruin a Reading
The Magnet Test and What It Actually Proves
Precious metals are diamagnetic: gold, silver and platinum are pushed away by a magnet, imperceptibly but consistently. The base metals that forgers reach for — iron, nickel — behave in the opposite manner and are pulled towards it with obvious force.
How the test works
Tilt the coin to about 45° and release a powerful neodymium magnet (N52) at the upper edge. Across genuine metal the descent is visibly retarded, nothing like the way the same magnet drops down a sheet of glass. Eddy currents circulating in the conductive metal are what hold it back.
Interpreting the results
Its limits: a copper or brass forgery is not magnetic either and will therefore pass without difficulty, while tungsten is drawn very slightly towards the magnet rather than repelled by it. The test eliminates candidates; it never confirms one. Its value lies entirely in what it contributes alongside weight and dimensions.
The Ping Test: What a Genuine Coin Sounds Like
Resonance is a property of the material, not of the design. Genuine precious metal answers a tap with a bright note that carries for two to five seconds; a filled or substituted coin swallows the vibration and produces a brief, dead sound instead.
Rest the coin on a fingertip or the tip of a pencil, touching it as little as you possibly can.
Strike the rim gently with a second coin or with a pencil.
Attend to three things — how long it sustains, how pure it sounds, how high it sits. A measuring app removes the guesswork.
Resonance by alloy type
Smartphone tools of the "CoinTest" and "Bullion Test" variety capture the note through the microphone and compare its frequency against stored references.
Hearing a tungsten core
Density is where tungsten resembles gold; stiffness is where it does not. A Young's modulus of 411 GPa against gold's 79 GPa is an enormous gap, and it translates directly into a higher resonance and a curter, harder sound. For that reason the ping test remains among the most trustworthy amateur methods of unmasking tungsten.
What Each Mint Does to Deter Forgers
Mints defend their products in different ways, and forgers stumble over different things as a result. Each card below sets out what to look for and where the copies typically fall down.
- Edge milled with 160 serifs
- Springbok cut with sharp definition
- Micro-text hidden in the hills from 2017
- Indistinct detail on the hooves
- A shade too yellow overall
- Serif count does not tally
- Laser-engraved DNA mark from 2014
- Radial lines radiating across the field
- The tightest weight tolerance in the market
- No micro maple leaf present
- Featureless background
- Weight quoted as 31.1 in place of 31.103
- Edge carrying 239 reeds
- Notch introduced with Type 2 in 2021
- Security devices the Mint does not disclose
- Off shade of gold
- No notch on the edge
- Liberty lacking relief
- Every orchestral instrument distinctly cut
- Organ pipes in raised relief
- Unmistakable 37×2 mm format
- Strings running into one another
- Incorrect edge bar
- Format does not match specification
- Latent image switching between castle and Britannia
- Encircling band of micro-text
- Surface Animation Technology
- Latent image fails to change
- Wave pattern refuses to move
- Micro-text nowhere to be found
- A fresh design every single year
- Fur rendered with genuine depth
- Temple of Heaven finely detailed
- Design belongs to a different year
- Fur reduced to a flat texture
- Temple detail indistinct
- Micro-engraving added from 2018
- Kangaroo motif redrawn annually
- Delicately worked fur
- Micro-feature simply missing
- Fur without definition
- Design inconsistent with the year
What the Risk Ratings Mean
Copied on an industrial scale. Take particular care with private sellers and with imports.
Forgeries circulate routinely; run at least two or three checks.
Copies exist but are not commonplace. Ordinary testing generally settles it.
Rarely targeted, either because the format is difficult or because demand is thin.
Laboratory Methods: XRF, Archimedes and Ultrasound
The home battery of tests — weight, dimensions, magnet, sound — disposes of most forgeries perfectly well. It is when the sum at stake is large, or the doubt persists, that laboratory methods earn their fee.
Identifies which elements are present in roughly the outermost 0.01 mm. An incorrect alloy is exposed immediately.
Compare the dry weight with the submerged weight and the density follows. Fine gold sits at 19.32 g/cm³, crown gold at 17.12 g/cm³.
Sound crosses gold at 3,240 m/s and tungsten at 5,220 m/s — a divergence of over 60 %, and impossible to disguise.
Worth remembering: above roughly €5,000, arrange an XRF reading before you part with the money. Reputable bullion dealers will usually run one at no charge or for a token fee.