Although duvet cover sizes may vary depending on manufacturer, various bedding stores such as Crane & Canopy, The Company Store and Bed Bath & Beyond offer duvet sizing charts on their websites. Crane & Canopy also offers a chart that detailed standard bed dimensions to help clarify sizing.
The Crane & Canopy mattress sizing chart is especially helpful for finding a correctly fitting duvet, as it gives the dimensions of standard North American mattresses. Comparing mattress sizes from this chart to the dimensions of the desired duvet helps ensure a correct fit. Duvets should cover comforters that are plus or minus 2 inches in dimension. Consulting the dimensions of the duvet and comparing them to the standard mattress size before purchasing makes it possible to buy the correct size.