Hello, the sheets are sewn for beds with a height of 30 cm. If your bed is larger than 30 cm in height, the sheet will still fit the corners of the mattress, but it will stretch a little more, leaving the sides slightly exposed. If you have a bed higher than 30 cm and the side opening bothers you, you can prefer a larger size. This time, there is a slight sag in the corners of the bed, but it comfortably covers all 5 surfaces of the bed. Finally, if the height of your bed is less than 30 cm, then you should take the exact size. If it is 140x200, it is 140x200, if it is 180x200, it is 180x200. We know that many people have developed the habit of buying larger sizes because the sheets they have received so far were too small, but since the sheets produced by our company are produced strictly adhering to universal sewing rules, this chronic problem is eliminated. We offer our respects. ELY PARKER.