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Last updated 4 May 2026 · Written by Connor Jones, Editor

How to Authenticate a Coin (UK Guide): The Six-Check Procedure

Counterfeit British coins exist at every price tier, from worn-bullion fake sovereigns to deceptive numismatic forgeries of Kew Gardens 50ps and 1933 pennies. Six home checks catch the majority of them in under two minutes; for coins worth £200 or more, professional grading is the only fully reliable test. This guide covers the full sequence with specifications for every modern UK denomination, plus the most-faked coins to watch for.

Last updated: 4 May 2026

In brief. Six checks: weight, dimensions, edge, magnetism, visual detail, anti-counterfeit features. Total kit cost under £50 (digital scale, calliper, loupe, magnet). A genuine coin passes all six. A competent fake usually fails at least two. For coins worth more than £200, send to PCGS, NGC or CGS UK; fees from £25 per coin are insurance against the cost of believing a forgery.

The home authentication kit

Tools first. The full kit is under £50 and lasts for life:

Digital scale, 0.1 g resolution. Around £15 from any kitchen-equipment retailer or jewellery supplier. Calibrate against a known weight (a 50p weighs 8.00 g; a 2p weighs 7.12 g) before use.
Digital calliper, 0.05 mm resolution. £15 to £25. Plastic-tipped jaws are gentler on coins than metal. Useful for diameter, thickness and rim measurements.
10x jeweller's loupe. Around £10. The single most useful tool. Higher magnification (20x, 30x) is overkill and harder to use.
Strong neodymium magnet. A 10 mm rare-earth magnet from any DIY store, around £5.
Daylight-balanced LED lamp. 5000K to 6000K colour temperature; positioned at low angle for raking light. Around £15.
Cotton or nitrile gloves. Optional but recommended for high-grade coins. Skin oils etch lustre.

Step 1: Weight check

Weight is the single most reliable home test. Every UK coin has a published Royal Mint specification with a tolerance of typically ± 0.05 g. A coin outside that window is almost certainly counterfeit or has been damaged (filed, holed, mounted then repaired).

Denomination	Type / years	Weight	Tolerance
1p	Bronze, 1971–1992	3.56 g	± 0.05 g
1p	Steel core, 1992–	3.56 g	± 0.05 g
2p	Bronze, 1971–1992	7.12 g	± 0.05 g
2p	Steel core, 1992–	7.12 g	± 0.05 g
5p	Cupronickel, 1990–2011	3.25 g	± 0.05 g
5p	Nickel-plated steel, 2012–	3.25 g	± 0.05 g
10p	Cupronickel, 1992–2011	6.50 g	± 0.05 g
10p	Nickel-plated steel, 2012–	6.50 g	± 0.05 g
20p	Cupronickel	5.00 g	± 0.05 g
50p	Cupronickel, 1997–	8.00 g	± 0.05 g
£1	Round, 1983–2016	9.50 g	± 0.10 g
£1	12-sided, 2017–	8.75 g	± 0.05 g
£2	Bimetallic, 1997–	12.00 g	± 0.05 g
Half sovereign	22 ct gold, 1817–	3.99 g	± 0.03 g
Full sovereign	22 ct gold, 1817–	7.988 g	± 0.05 g

Reference: Royal Mint coin specifications. Older pre-decimal denominations have separate published weights; consult Spink Standard Catalogue for those.

Step 2: Dimension check

Diameter and thickness rule out cast counterfeits. The casting process introduces 0.1 to 0.3 mm of shrinkage as the metal cools, so most cast fakes run measurably undersized. Modern struck counterfeits are usually within 0.1 mm but rarely match all dimensions exactly.

Denomination	Diameter	Thickness
1p	20.3 mm	1.65 mm
2p	25.9 mm	1.85 mm
5p	18.0 mm	1.7 mm
10p	24.5 mm	1.85 mm
20p	21.4 mm	1.7 mm
50p	27.3 mm (across flats)	1.78 mm
£1 round (1983–2016)	22.5 mm	3.15 mm
£1 12-sided (2017–)	23.43 mm point-to-point	2.8 mm
£2	28.4 mm	2.5 mm
Half sovereign	19.30 mm	1.0 mm
Full sovereign	22.05 mm	1.52 mm

Use the calliper's plastic-tipped or rubber-tipped jaws where possible. Steel jaws can leave faint marks on high-grade surfaces.

Step 3: Edge inspection

The edge is where casting and low-grade striking show the fastest. Inspect under direct light, rotating the coin slowly:

Reeded (milled) edge — 50p, 5p, 10p, 20p, half and full sovereign. The reeding should be sharp, even and uniform from one face to the other. Soft, blurred or interrupted reeding indicates a cast fake. Look specifically for any horizontal seam line where the two halves of a casting mould met.
Plain edge — 1p, 2p. Look for a sharp clean meeting between obverse and reverse rim. Cast fakes often show a faint seam.
Lettered edge — £2 (varies by design), some commemorative crowns and proofs. The lettering must be incuse (recessed), sharp and evenly spaced. Smudged or raised lettering is a clear fake.
Twelve-sided edge — new £1 (2017+). Should have six milled flats alternating with six smooth flats. Continuous milling or all-smooth indicates a fake.

Step 4: Magnetism test

Most UK coins are entirely non-magnetic. The exceptions are post-1992 steel-core 1p, 2p, 5p (post-2012) and 10p (post-2012). Knowing what the coin should do is the key to interpreting the test.

Denomination / period	Composition	Magnetic?
1p / 2p, 1971–1992	Bronze (97% copper)	No
1p / 2p, 1992–	Copper-plated steel	Yes (by design)
5p / 10p, pre-2012	Cupronickel	No
5p / 10p, 2012–	Nickel-plated steel	Yes (by design)
20p, all years	Cupronickel	No
50p, all years	Cupronickel	No (any magnetic 50p is fake)
£1 round (1983–2016)	Nickel-brass	No
£1 12-sided (2017–)	Bimetallic, nickel-brass + nickel-plated alloy	No
£2 (1997–)	Bimetallic, cupronickel + nickel-brass	No
Sovereign / half sovereign	22 ct gold	No (any magnetic sovereign is fake)
Britannia (silver)	.999 silver	No

A Kew Gardens 50p that sticks to a magnet is fake. A 1990 2p that sticks is fake (bronze era). A 1995 2p that sticks is genuine (steel era). Always confirm the year before drawing conclusions.

Step 5: Visual inspection under a 10x loupe

The loupe catches what numbers and magnets miss: design detail, font consistency, surface texture and tooling marks. Compare the coin in hand to a known-good reference image (Royal Mint website, Spink Standard Catalogue, our coin browser). Look specifically for:

High-point detail. Cast counterfeits lose definition at the highest points of the design (the monarch's ear and hair, Britannia's shield, St George's sword). On a genuine coin, even worn examples retain clean if shallow detail. On a cast fake, the high points are mushy at any grade.
Font and legend. Royal Mint legends use specific typography that is consistent across denominations and reigns. Counterfeit fonts are often subtly different: serifs, letter spacing, decimal-point placement. Compare the "ELIZABETH II" or "CHARLES III D G REG F D" legend against a reference.
Surface texture. Genuine struck coins have a smooth, slightly directional flow texture under magnification. Cast fakes show a uniformly rough or pitted surface. Pressed-die counterfeits often show repeated minute imperfections that betray a master die.
Repaired holes or tooling. Look for any small circular smoothed area suggesting a previous hole has been filled and re-engraved. Also look for tooling marks (parallel scratches) where detail has been "improved" by an engraver.
Toning consistency. Natural patina forms gradually and consistently across the coin. Splotchy, patchy or unnaturally bright areas suggest cleaning, dipping or selective re-toning.

Step 6: Anti-counterfeit features

Modern UK coins increasingly carry overt and hidden security features. Verify each:

12-sided £1 (2017–). Tilt under direct light: the small hologram between the year and central design must switch crisply between "£" and "1". Static or printed-looking holograms are fake. Under a 10x loupe, micro-lettering around the lower edge of both faces should be sharp and individual. Full procedure in our fake £1 guide.
£2 bimetallic (1997–). Edge inscription varies by design (e.g. "STANDING ON THE SHOULDERS OF GIANTS" on the Newton design); should be incuse, sharp and evenly spaced.
Salmon 50p (2023, Charles III). Fine scale detail on the salmon under 10x; mintmark privy mark in upper-left field on first-issue strikes. The detail is too fine for casual counterfeits.
Olympic 50p (2012). Each design has consistent low-relief sport-specific detail; the Football design carries the offside-rule diagram. Look for crispness in the small text and lines.
Modern proof and BU sets. Royal Mint Brilliant Uncirculated and proof issues come in sealed packaging with certificates of authenticity. Loose proofs without packaging warrant additional scrutiny.

When to use professional authentication

The home six-check sequence is sufficient for the majority of modern UK coinage. Three situations call for professional grading:

The coin is worth £200 or more. The grading fee (£25 to £50) is small relative to the price uplift the slab provides (10 to 30 per cent on rarities) and removes any authentication doubt at sale.
The coin is contentious or borderline. If any of the six home checks gives an ambiguous result, professional examination under microscope and reference-comparison resolves it.
The coin is hammered, ancient or unfamiliar. Roman, Greek and medieval hammered coinage requires specialist authentication beyond the home kit. Use a numismatic specialist (Spink, Baldwin's) or specialist grading services for ancients.

Service	Country	Standard fee	Turnaround	Strengths
PCGS	USA, UK submission via approved dealers	From £30 per coin	Roughly 6 to 8 weeks	International resale; US coins; premium UK rarities
NGC	USA, with London office	From £30 per coin	Roughly 4 to 8 weeks	General-purpose; UK drop-off available
CGS UK	UK	From £20 per coin	Roughly 4 to 6 weeks	British coinage; lower-value submissions

Fees and turnaround change frequently; always check the current published rates before submitting. Full submission procedure in our how to get a coin graded guide.

Most-faked British coins (and what to look for)

Counterfeit production concentrates on coins where the price is high enough to justify the forging effort. The current top of the list:

Coin	Genuine value	Most common fake tell
Kew Gardens 50p (2009)	£120 to £400	Underweight (typically 7.6 to 7.8 g vs 8.00 g); soft pagoda step detail
Undated 20p (2008 mule)	£60 to £150	Cast surface texture; weight off by 0.1 g+
1933 penny	£60,000+	Surface tooling; doubled lettering from die transfer; die alignment off
Edward VIII pieces	£20,000+ for genuine; most are fantasy	Most "Edward VIII" coins are fantasy strikes; only six denominations were officially produced and most are in museums
2002 Commonwealth Games NI £2	£25 to £80	Wrong-flag Commonwealth £2s appear; check the small flag on the reverse matches the country
High-grade common-date sovereigns	Bullion + 5 to 15%	Underweight (under 7.93 g); magnetic; soft St George detail; seam line on edge
12-sided £1	£1	Hologram static or absent; weight under 8.70 g; soft edge milling
Charles I crowns and half-crowns	£300 to £5,000+	Surface texture; lettering inconsistent with reference; cast seam
Roman silver and gold (denarii, aurei)	£20 to £20,000+	Tooled surfaces; modern strike characteristics; specialist authentication required

Frequently asked questions

How can I tell if a UK coin is genuine?

Six home checks catch most counterfeits: weight on a 0.1 g scale, diameter and thickness with a digital calliper, edge inspection, magnet test (most UK coins are non-magnetic), 10x loupe inspection of design detail, and verification of any anti-counterfeit features such as the 12-sided £1 hologram. A genuine coin passes all six; a competent fake usually fails at least two. For coins worth £200 or more, professional authentication from PCGS, NGC or CGS UK is the only fully reliable test.

Are most fake UK coins easy to spot?

For mass-produced counterfeits aimed at circulation, yes. Cast or low-grade struck fakes typically fail two or three checks immediately: undersized weight, soft edge milling, missing micro-text. Deceptive numismatic forgeries are harder. Fake Kew Gardens 50ps, undated 20ps and high-grade sovereigns are now well-made enough to pass a casual visual inspection; only weight, dimension and design-detail comparison reliably catches them. Always perform the full sequence, not just the obvious test.

What weight should a genuine UK coin be?

Each denomination has a published Royal Mint specification with a tolerance of around ± 0.05 g. A 50p is 8.00 g, the 12-sided £1 is 8.75 g, the £2 is 12.00 g, the modern penny is 3.56 g (steel core, post-1992) and the modern 2p is 7.12 g. The full sovereign is 7.988 g. Coins outside the tolerance window are off-spec. A 0.1 g resolution kitchen or jewellery scale (around £15) is sufficient.

Can a magnet really tell if a coin is fake?

For most UK denominations, yes — with one important exception. Cupronickel coins (5p, 10p, 50p), bronze pre-1992 pennies and 2p, and gold sovereigns are all entirely non-magnetic. Steel-core 1p and 2p (post-1992) are magnetic by design. So if a Kew Gardens 50p sticks to a magnet, it is fake; if a 1990 2p sticks, it is genuine. Always know what the genuine coin should do before drawing a conclusion.

What tools do I need for at-home coin authentication?

A digital scale (0.1 g resolution, around £15), a digital calliper (0.05 mm resolution, £15 to £25), a 10x jeweller's loupe (£10), a strong neodymium magnet, and a daylight-balanced LED lamp. Total kit: under £50. With these, you can run the full six-point check in under two minutes per coin. For coins worth more than £200, kit is no substitute for professional grading.

How do I authenticate a sovereign?

Five tests: (1) weight 7.988 g ± 0.05 g; (2) diameter 22.05 mm; (3) sharp uniform reeded edge with no seam; (4) entirely non-magnetic; (5) crisp Pistrucci St George reverse with sword tip clearing the dragon's wing. For high-value or rare-date sovereigns, professional authentication from PCGS, NGC or CGS UK at £20 to £40 per coin is the only reliable option. The full procedure is in our sovereign values guide.

Are eBay coins risky to buy?

Riskier than buying from a BNTA-member dealer or specialist auction. Counterfeit Kew Gardens 50ps, undated 20ps and Charles I crowns appear on eBay regularly. Mitigations: prefer slabbed (PCGS, NGC, CGS UK) listings, check seller feedback specifically for coin sales, request additional photos including the edge, and use eBay's buyer protection (return within 30 days for "not as described"). Avoid raw high-value coins from new sellers regardless of price.

How do I verify a Kew Gardens 50p is real?

Four checks. (1) Weight: 8.00 g ± 0.05 g; counterfeits typically run 7.6 to 7.8 g. (2) Diameter: 27.3 mm; check with calliper. (3) Magnet: cupronickel is non-magnetic; if it sticks, it is fake. (4) Design detail under 10x loupe: the pagoda steps should be sharp and even, the climbing plant tendrils crisp. The full procedure is in our Kew Gardens 50p guide. Counterfeits are common — always check.

Which UK coins are most commonly faked?

In rough order of counterfeit prevalence: Kew Gardens 50p (Britain's most famous modern rarity), undated 20p (2008 mule), 1933 penny, Edward VIII pieces (most are fantasy), 2002 Commonwealth Games Northern Ireland £2, high-grade sovereigns of common dates, and 12-sided £1 (rare but exists). Hammered medieval and Roman coins are also widely counterfeited and require specialist authentication beyond home checks.

Should I send every old coin for professional authentication?

No. Authentication fees of £25 to £50 per coin only make sense where the coin's expected value exceeds roughly £200. Below that, the fee outweighs the uplift. For lower-value coins, the home six-check sequence is sufficient. Save professional submission for high-value, rare-date or otherwise contentious pieces where a slab adds 10 to 30 per cent to resale value. See our grading submission guide.

What is "specific gravity" testing and do I need it?

Specific gravity (SG) tests the density of a coin against a reference value for the genuine alloy. It involves weighing the coin in air and submerged in water, and dividing. Gold sovereigns should give 17.7 to 17.9; silver crowns 10.3 to 10.5; cupronickel 8.9 to 9.0. SG is excellent for detecting tungsten-cored fake gold coins, which match weight but not density. Most home authenticators do not need it; for high-value gold, it is a useful additional check.

How can I check a coin's edge inscription?

Hold the coin sideways under direct daylight and rotate slowly. UK coins with edge inscriptions include the £2 (varies by design, e.g. "STANDING ON THE SHOULDERS OF GIANTS" on the Newton design), some commemorative crowns and several proof issues. The lettering should be incuse (recessed), sharp and evenly spaced. Smudged, raised or absent inscription is a clear counterfeit tell. Reeded-edge coins (50p, sovereign) should show uniform sharp reeding with no seam.