The territory of the islands of Britain and Ireland was inhabited by people in prehistoric times. Numerous megalithic monuments remain from this culture. In the first millennium BC, Celtic tribes moved there from continental Europe, who later mixed with the local population. The maritime trade of the ancient civilisations of the Mediterranean with the population of the British Isles is reported by some historical sources of the antiquity. This trade was conducted by exchanging goods for goods. There is no information in historical sources about the measures, in particular weights, used by the ancient population of the British Isles in production and trade. In the first century BC, the Romans conquered the territory of Britain. They established their own system of measures, including weights, and their own monetary system. After the fall of the Roman Empire in the V century, Germanic tribes such as the Angles, Saxons, and Utes invaded Britain. At first, they created several kingdoms here, and in the IX century, they united into a single Anglo-Saxon state. It was during the Anglo-Saxon period from the V to the XI centuries that the foundations of the modern British System of Measures and Monetary System were laid. In the formation of the British weight system, units of weight measures of the Celts, Romans and Germans were used. Norms of weight measures were approved in the laws of the Anglo-Saxon kings of the X–XI centuries, which have survived to this day. The conquest of Britain in 1066 by the Norman Duke William did not make changes to the system of weight measures used here. Over the centuries, from time to time, for the purpose of improvement, royal decrees and laws amended these measures. The transformation of the weight measurement system for a thousand years can be studied precisely by analysing the materials of English legislation. In the XVI–XX centuries, Great Britain became a colonial power, whose possessions covered vast territories in the North America, Africa, Asia and Oceania. Here, the colonial administration introduced the British system of weight measures, but the local population used their own measures along with the British ones. After the gradual disintegration of the British colonial empire, some new states that were formed on the site of its former possessions – the USA, Canada, Australia, and New Zealand – continued to use British standards of weight measures. The British system of weight measurements is made public in the USA. Nowadays, the British system of weight measures, along with the metric, is officially considered the state in the United Kingdom.