High Quality Content by WIKIPEDIA articles! The British Five Guinea coin was a machine-struck currency produced from 1668–1753. It was a gold coin 37 millimetres in diameter and weighing between 41 and 42 grams. Although the coin is now known as the "five guinea" piece, during the 17th and 18th centuries it was also known as a five pound piece, as during the reign of Charles II a guinea was worth twenty shillings — until its value was fixed at twenty-one shillings by a Royal Proclamation in 1717 the value fluctuated rather in the way that bullion coins do today.