Coin weight identification: square, round and guinea weights dated

A small, thick brass square. A crowned figure on one side. On the other, a crown over XXS.

That’s not a coin. It’s a coin weight, and it tells you exactly which gold coin it was made to check.

What a coin weight did

Gold coins were worth their weight. Clip a sliver off the edge, or let a coin wear thin, and it was worth less than its face value.

So traders weighed them. The coin went on one pan of a small balance, the coin weight on the other. Light coin, no deal.

Statutes mention coin weights, or “penny-poises”, as early as 1205, under King John. But no official weights are known for the silver penny. Every known English coin weight is for a gold coin, until the reign of Charles I (1625 to 1649).

How to recognise one

• Small and thick, cast or struck, usually copper alloy.
• Round or square. Square is the giveaway for the 16th and early 17th centuries.
• One side copies the design of the coin: a king in a ship, St Michael and the dragon, a king enthroned, a bust.
• The other side, from Henry VIII on, often shows the value in shillings (S) and pence (D), in Roman numerals, under a crown.
• Early weights are uniface, with a design on one side only.

If it has a value like XXS, VS or IIS VID, you’re almost certainly holding a coin weight.

Dating by shape

The shape alone narrows it down a lot.

Why the 1632 ban? Parliament said many square weights in use were “too heavy, and others too light, so that men bought and received by one weight, and sold and delivered by another”.

The round replacements were made by Nicholas Briot, the Mint’s chief engraver. Many carry his initial B. They’re among the most common coin weights found.

Which coin? The main designs

Match the design and value to the coin.

Two useful tells:

• The Angel. Known weights all show St Michael with both feet on the dragon, the design revised in 1491.
• The 1612 revaluation. Gold was raised 10% in 1612. A James I weight reading XXIIS, XIS, VS VID or IIS IXD is from after that date. These are more common than the earlier XXS, XS, VS weights.

Guinea weights

Guinea weights are numerous. The Guinea was first struck in 1663 and its weight was fixed at 129½ grains (about 8.4 g) after 1670.

Until George III, most show the reigning monarch’s head on one side and a crown over crossed sceptres with 1 GUINEA W. on the other. From William III’s reign some makers put their name or initials by the bust, or in place of it. From 1746 you’ll see I.K. or JOHN KIRK under the bust.

Look for an ewer or coffee-pot stamp. That’s the mark of the Founders Company, often found on guinea weights of this period.

The 1774 figures

By the 1770s many guineas had been circulating for a century and were light. A 1774 Proclamation set different values for guineas by age, so weights from after it often carry the value and the weight in pennyweights (dwt) and grains (gr).

A pennyweight is 24 grains. So 5 dwt 9 gr is 129 grains, the full guinea. UKDFD says the 20s 6d and 20s 10d types are the ones most often found, along with the 21s value.

You’ll also see phrases such as “1771 OR OLDER”, “COINED BEFORE 1772” and “TO THE NEW STANDARD”.

A real example: a PAS-recorded weight from Swaffham, Norfolk, reads 20:6 and Dwt Gr 5:6. It’s a guinea weight for the 20s 6d tier. Its recorded weight is 7.5 g.

Certification marks

A 1775 Act required coin weights to be tested and stamped if correct. The marks were:

• an ewer for the Founders Company of the City of London;
• the Imperial crown for the Royal Mint;
• an anchor for Birmingham;
• a lion passant for London.

Earlier marks include a crowned E for Elizabeth I (ordered in 1587) and a crowned I for James I.

The Coinage Act of 1891 guaranteed the value of each new coin and made coin weights for single coins obsolete.

Weigh it, but don’t rely on it

A coin weight was meant to match its coin. In practice, a weight can come out of the ground lighter than it went in, and some were never right. A PAS-recorded William III guinea weight, for example, weighs 7.9 g against the guinea’s 8.4 g.

So identify by design and value first. Use the weight as a check. Our hammered coins guide covers the coins themselves. Brass discs with no value but a design and legend are more likely jetons, the reckoning counters.

Record it

Coin weights are copper alloy and aren’t coins, so they’re not usually Treasure. Since 30 July 2023 a metal object over 200 years old can be Treasure if it’s of exceptional significance. See what counts as treasure.

They’re still worth recording with your Finds Liaison Officer. A coin weight is a sign that someone handled gold in that spot. More object guides are in the Find ID drawer.

FAQ

What is a coin weight?

A small weight, usually copper alloy, made to the legal weight of one particular gold coin. A trader put the coin on one pan of a balance and the weight on the other. If the coin was lighter, it had been clipped or worn and wasn't worth face value.

How do I tell which coin it's for?

Look at the design and the value. The design usually copies the coin: a king in a ship for a Noble, St Michael and the dragon for an Angel. From Henry VIII onwards the reverse often gives the value in shillings and pence in Roman numerals, such as XXS for 20 shillings or XIS for 11 shillings. Guinea weights usually say GUINEA.

How old is my coin weight?

Square ones are mostly 16th century up to 1632, when an Act banned them. Round ones with James I or Charles I coins and Briot's ‘B’ were made after 1632. Guinea weights run from the late 17th century to 1821, and ones with dwt and gr figures follow the 1774 Proclamation.

Why is my coin weight lighter than the coin?

Wear and corrosion can take weight off, and not every weight was accurate to begin with. In 1632 Parliament complained that many square weights were too heavy and others too light. Use the design and value to identify it, not the weight alone.

Is a coin weight Treasure?

Almost never. They're copper alloy, not gold or silver, and they aren't coins. Under the 2023 significance class a metal object over 200 years old can be Treasure if it's of exceptional significance, so record unusual ones with your Finds Liaison Officer.

Sources

Every figure in this guide comes from one of these. We checked each one on 3 November 2026.

1. C. J.'s Metal Detecting Pages, “Coinweights for English Gold Coins”, parts 1 and 2 (UK Detector Finds Database, 2002), citing R. Ruding, Annals of the Coinage, and L. A. Lawrence. www.ukdfd.co.uk/ceejays_site/pages/Coinweight1.htm
2. C. J.'s Metal Detecting Pages, “Coinweights for English Gold Coins: The Guinea” (UK Detector Finds Database, 2002). www.ukdfd.co.uk/ceejays_site/pages/Coinweight2.htm
3. Portable Antiquities Scheme, record LANCUM-CA0A4C, copper-alloy guinea coin weight of William III. finds.org.uk/database/artefacts/record/id/619742
4. Portable Antiquities Scheme record via Archaeology Data Service: copper-alloy guinea weight of George III, Swaffham, Norfolk (S D 20:6, Dwt Gr 5:6; 7.5 g). archaeologydataservice.ac.uk/data-catalogue/resource/e1403cc659bef9837acfe6caa77d377beb7d047e3f9a2a3e807318c40b80091e
5. Portable Antiquities Scheme record via ARIADNE: cast copper-alloy guinea weight of William III, Cheriton, Hampshire (7.9 g). ariadne-portal-staging.d4science.org/resource/043181d4a8678a3a1001f9ac4a5c08cd2573b94663e8057e8d8be54d062485a1
6. DCMS, The Treasure Act 1996 Code of Practice (3rd revision, 2023), GOV.UK. www.gov.uk/government/publications/treasure-act-1996-code-of-practice-3rd-revision