How to Identify the Third Guinea

What Is It

The Third Guinea is a small British gold coin representing one-third of a guinea, equal to seven shillings. It was introduced in 1797 under George III, during a period when larger gold coins were being hoarded and melted due to wartime economic pressures, prompting the Royal Mint to issue smaller, more practical gold denominations. Production continued intermittently through 1813, shortly before the guinea system was replaced by the sovereign in 1816-1817.

Obverse Design

The obverse shows George III's bare head facing right, with the surrounding legend GEORGIUS III DEI GRATIA, in the same plain neoclassical style used on other late George III gold coinage.

Reverse Design

The reverse displays a crowned, garnished shield bearing the royal arms, with the date positioned around or below the shield and the remainder of the Latin royal title completing the legend. Unlike the guinea and half guinea, the Third Guinea's small size means its heraldic details are noticeably compact and less detailed.

Size, Weight, and Metal

The Third Guinea is struck in 22-carat gold, weighs roughly 2.8 grams, and measures about 17mm in diameter, making it a notably thin and small coin. Its light weight and small size mean it is easily bent, scratched, or worn.

Mint Marks and Where to Find Them

All Third Guineas were produced at the Royal Mint in London and carry no branch mint marks. Identification relies on reading the date, which sits close to the shield due to the coin's limited space.

Telling It Apart from Similar Coins

The Quarter Guinea is even smaller and thinner and was struck only in 1718 and 1762, so any coin of this general style dated between 1797 and 1813 is almost certainly a Third Guinea rather than a Quarter Guinea. The Half Guinea, by contrast, is visibly larger and heavier, providing an easy size comparison when the two are placed side by side.

Judging Condition at a Glance

Wear shows first on George III's hair and cheek on the obverse, and on the raised curves of the crown and shield on the reverse. Because these coins are thin and were carried loosely in pockets and purses, finding one with sharp, undamaged rims and full original luster is less common than finding a worn, bent, or lightly creased example.

Authenticity Red Flags

Given their small size and gold content, Third Guineas have sometimes been targeted for lightweight cast reproductions; a genuine piece should weigh close to 2.8 grams and show crisp, well-defined lettering despite its small size. Excessive softness in the design, an incorrect diameter, or a weight noticeably below the expected figure are signs of a copy rather than an original mint product.