Is Your Bullion Coin Genuine? Free Authenticity Calculator
What to Buy
£25–70 · resolves to 0.01 g at minimum, 0.001 g ideally
£15–35 · good to ±0.02 mm, covers diameter and thickness
£5–10 · for the slide test on diamagnetic metals
Note: What you get here is a physical plausibility check, not a laboratory report. XRF and ultrasound examine things a scale and a caliper cannot reach, and for a coin of real value that examination is worth paying for. Remember too that UK hallmarking law covers bars and jewellery but exempts legal-tender coinage, so a Sovereign carries no assay office mark and its absence proves nothing.
Weight alone, with mint tolerances and a traffic-light verdict.
Diameter and thickness assessed on their own.
Metal content value for bars, coins, alloys and scrap jewellery.
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Enjoying what you see and read?
We pour our heart into keeping preciousmetalprices.com fast, clean and free — no paywalls, no clutter, just reliable facts and live prices. If it helps you, the nicest way to say thank you is to pass it on. Every share helps a fellow investor discover us and keeps the project going. 💛
Checking a Bullion Coin at Home — The Complete Guide
Record gold prices have made forgery worth the forger's while as never before. Fortunately the counterfeiter has one adversary he cannot negotiate with: physics does not bluff. Mass, width and height are locked together by the density of the metal, and a coin that satisfies all three at once has almost nowhere left to hide a substitute material.
Five checks, in the order that makes sense
Look at the strike, the fine detail, the milling and the colour.
Set it on a 0.01 g scale and compare against the specification.
Caliper across the face, then through the middle.
Tilt the coin and let an N52 magnet run down it.
Strike the rim — a genuine coin rings on and on.
The whole kit for under £100
Three inexpensive instruments, and between them they close the door on more than 95 % of the fakes in circulation.
Density — The One Property a Forger Cannot Fake
Density is a fingerprint. Swap the metal but keep the mass, and the volume has to change with it — which means the coin can no longer be the right size.
Worked Example: A Copper Fake
Work it through with copper. A genuine 1 oz gold coin packs 31.103 g into about 1.61 cm³. To reach the same mass, copper at 8.96 g/cm³ needs roughly 3.47 cm³ — more than twice the space. The disc ends up around 4.3 mm deep rather than 2.8 mm, which the cheapest caliper on the market will spot instantly.
Tungsten — the one that gets close
One metal comes uncomfortably close: tungsten, at 19.25 g/cm³, sits within 0.36 % of gold. Mass and dimensions can both come out right, so the physical checks alone will not settle it.
Official Figures and Permitted Tolerances, Coin by Coin
Ten of the world's most heavily traded 1 oz bullion coins are listed below with their official figures. Weight, diameter and thickness are precisely the three quantities the calculator above works with. The column marked tolerance is the mint's own permitted margin — land anywhere inside it and the coin is on specification.
| 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 |
Figures refer to the 1 oz versions throughout (the Sovereign being the exception at 7.988 g). Tolerances follow the specifications published by each mint. For weight on its own, with a traffic-light reading, use the Weight Checker.
Using a Caliper Properly — Three Steps
After the scale, nothing earns its keep faster than a digital caliper. Thirty pounds buys ±0.02 mm of resolution, which is more than enough to catch any dimensional error that matters.
Shut the jaws fully and press ZERO. Wipe the faces first — clean and dry, always.
Grip the coin in the outer jaws so the line passes through the centre. Turn it 60° and repeat twice more, then average.
Use the depth faces, in the middle of the coin rather than near the rim. Again, three readings and an average.
Where Measurements Go Wrong
The Magnet Test — Thirty Seconds and Ten Pounds
Iron and nickel jump at a magnet. Gold, silver and platinum do the opposite: they are diamagnetic and are nudged very slightly away. That single difference disqualifies a whole family of cheap forgeries in seconds.
How the test works
Prop the coin up at roughly 45° and set a strong neodymium magnet (N52) at the top of the slope. On real precious metal it creeps down as though through treacle, dramatically slower than the same magnet on glass. The braking comes from eddy currents induced in the conductive metal.
Interpreting the results
Where it stops working: copper and brass are non-magnetic too, so a copper forgery sails through, and tungsten is faintly paramagnetic rather than repelled. Treat the magnet as a way of ruling material out, never as confirmation — it only means anything alongside weight and dimensions.
Listening to the Coin — The Ping Test
Struck properly, a genuine bullion coin sings: a clear note lasting two to five seconds. Forgeries answer with a short, flat clack, because every material resonates at its own frequency and base metals damp the vibration quickly.
Balance the coin on a fingertip or the end of a pencil so that almost nothing touches it.
Give the rim a light knock with a second coin or a pencil.
Judge how long it rings, how clean the note is and how high it sits. A phone app measures it properly.
What the different alloys sound like
Applications such as "CoinTest" and "Bullion Test" pick the note up through the handset microphone and match it against stored reference frequencies.
Catching tungsten by ear
Here is where tungsten finally gives itself away. Its density may match gold, but its stiffness does not come close — a Young's modulus of 411 GPa against gold's 79 GPa. The result is a measurably higher resonance and a shorter, harder note, which makes the ping test one of the most dependable ways of catching a tungsten core at home.
Security Features and Forgery Risk, Coin by Coin
No two mints protect their coins the same way. The cards below pair the details worth looking for with the flaws forgers keep repeating.
- 160 serrations on the milled edge
- Crisply defined springbok
- Micro-lettering in the hills (2017 onwards)
- Hooves rendered soft or vague
- Colour running too yellow
- Serration count off
- Laser-cut micro maple leaf (2014 onwards)
- Radial lines across the field
- Narrowest weight tolerance of any bullion coin
- No micro leaf under magnification
- Field left plain
- Mass given as 31.1 rather than 31.103
- 239 reeds around the edge
- Notched edge on the Type 2 (2021 onwards)
- Undisclosed anti-counterfeiting devices
- Colour tone slightly wrong
- Edge notch absent
- Liberty rendered too flat
- Instruments picked out individually
- Raised organ-pipe relief
- Unusual 37×2 mm proportions
- Strings blurred together
- Edge bar incorrect
- Dimensions off specification
- Latent image alternating castle and Britannia
- Ring of micro-lettering
- Surface Animation Technology in the field
- Latent image does not switch
- Waves that stay static when tilted
- Micro-lettering missing
- Design redrawn every year
- Fur modelled in three dimensions
- Temple of Heaven rendered sharply
- Design does not match the stated year
- Fur flattened out
- Temple detail smeared
- Micro-engraving (2018 onwards)
- New kangaroo motif each year
- Fur worked in fine relief
- Micro-feature absent
- Fur detail indistinct
- Motif wrong for the year struck
Risk Levels — How to Read Them
Forged in quantity. Be especially wary of private sales and of coins arriving from abroad.
Fakes turn up regularly. Run two or three tests before you settle.
Known forgeries exist but are uncommon. The standard checks normally suffice.
Seldom worth a forger's effort — awkward to copy, or too little demand.
Beyond the Kitchen Table — XRF, Archimedes and Ultrasound
Scale, caliper, magnet and ear will see off the great majority of forgeries. Once the sums get large or the doubt refuses to go away, it is time for instruments you do not own.
Reads the elemental make-up of roughly the top 0.01 mm. A wrong alloy shows up straight away.
Weigh dry, weigh submerged, derive the density from the difference. Pure gold reads 19.32 g/cm³; crown gold reads 17.12 g/cm³.
Times sound through the metal: 3,240 m/s in gold against 5,220 m/s in tungsten — a gap of more than 60 %.
Rule of thumb: once a purchase passes £5,000, have an XRF reading taken before the money moves. Most established bullion counters run the test on request, free or for a nominal charge.