A double duvet is usually 200 x 200 centimeters or 79 x 79 inches. This size is a good middle ground for a duvet for two people. However, it is important to measure your bed frame or mattress to ensure that a double duvet is the right size for your bed. Other common UK duvet sizes include single (135 x 200 cm), king (230 x 220 cm), and super king (260 x 220 cm) . It is worth noting that duvet sizes may vary slightly depending on the manufacturer or brand.