For a perfectly made bed, it is important to know the size of your mattress. Your mattress has a width and length. The height must also be determined. You can choose a fitted sheet with different corner heights. The standard corner height is 30 cm. Take into account any Featherbed and/or topper that you place on the mattress. This will ultimately determine the height of your fitted sheet. For the Featherbed or a standard topper you should choose a corner height of 40 cm.