In the UK, a size 12 typically refers to women's clothing and is considered a medium size. It generally corresponds to a bust measurement of 36 inches, a waist measurement of 28 inches, and hip measurement of 38 inches. This sizing system is commonly used in various clothing brands and retailers across the country. It's important to note that sizing can vary between different brands and styles. Therefore, a UK size 12 in one brand may fit differently than in another. Many retailers provide size charts to help customers find the best fit for their body shape and measurements.