There are no industry-wide standard sizes for bed blankets, but most blankets will fall within a few centimetres of the approximate sizes. These sizes will help you select or make the best blankets to fit your bed.
Single beds are 90 cm by 190 cm (39 inches by 76 inches), and their blankets are generally 170 cm by 215 cm (68 inches by 86 inches for comforters. Down comforters can be longer, at 170 cm by 220 cm (68 inches by 88 inches), and regular blankets tend to be 165 cm by 225 cm (66 inches by 90 inches).
Double beds are 135 cm by 190 cm (54 inches by 76 inches), and blankets and comforters for double beds are usually about 200 cm by 225 cm (78 inches by 90 inches). Many blankets are sold as a full/queen size instead, at 220 cm by 220 cm (88 inches by 88 inches), or 225 cm by 225 cm (90 inches by 90 inches). Full/queen down comforters are closer to 225 cm by 245 cm (90 inches by 98 inches).
At 150 cm by 200 cm (60 inches by 78 inches), the king bed can use full/queen blankets in addition to its own sizes. When available, king blankets are about 215 cm by 235 cm (86 inches by 94 inches).
Eastern king bed
The eastern king bed, at 200 cm by 200 cm (78 inches by 78 inches), has comforters measuring about 275 cm by 240 cm (110 inches by 96 inches), down comforters at 270 cm by 245 (108 inches by 98 inches), and regular blankets at 270 cm by 225 cm (108 inches by 90 inches).
Other bed sizes
Extra-long twin mattresses require fitted sheets in their exact sizes, but it is rare to find blankets designed for these sizes of mattresses. Single bed blankets will work fine on an extra-long single bed.