All boombeds are Duvet Covers that will fit over existing Comforters or Down Duvets. The sizes here are the guides for the Twin (also single) or Queen (also Full/Double) sizes. The snug of the fit will depend on your underlying comforter, with the size of the duvet covers as follows:
Twin : 64" x 86" | Queen: 86" x 86"
Twin : 164cm x 218cm | Queen: 218cm x 218cm