To determine the size of tablecloth you need, you should measure the length and width of your table and add twice the desired drop to each sides dimension. The drop is the length of the tablecloth that hangs over each side of the table, and it depends on the formality of the occasion. For casual events, tablecloths should have a 6- to 8-inch drop from the edge of the table to the bottom of the tablecloth, while for more formal events, the best choice is a tablecloth that has a 15-inch drop from the edge of the table to the bottom of the tablecloth. Once you have the dimensions of your table and the desired drop, you can use a tablecloth size calculator or a tablecloth sizing chart to find the closest standard size that matches your tabletop dimensions. If you cant find the exact size you want, you can size up to the next available size. For round tables, you should measure the diameter of your table and add twice the desired drop to determine the tablecloth size you need.