That would depend on the depth of your mattress. We recommend buying bigger than the depth of your mattress to allow the needed tuck under to keep your fitted sheet in place. As mattresses get deeper with the addition of mattress toppers, protectors, we need sheets to allow for a good snug fit and avoid the common problem of sheets coming off during the night. We recommend your extra deep fitted sheet to sit 8cm (2-3 inches) deeper than your mattress. Our fitted sheets are generously elasticated around all 4 corners leading to a solid hold and fit on your mattress. 

If your fitted sheet is coming untucked when slept on then you probably have the wrong size depth for your mattress. Note that the box depth on your fitted sheet, needs to be deeper than your mattress. As mattresses get deeper with the addition of mattress toppers, protectors, we need sheets to allow for a good snug fit and avoid the common problem of sheets coming off during the night. We recommend your fitted sheet to sit 8cm (2-3 inches) deeper than your mattress. Our fitted sheets are generously elasticated around all 4 corners leading to a solid hold and fit on your mattress. 

If your mattress depth is deeper than a 10 inch depth, or you prefer a mattress topper on your bed, a deeper fitted sheet is recommended to allow an adequate tuck under.