According to your upper and lower bust, you can calculate your underwear cup size through the following steps: First, calculate the difference between upper and lower bust: 88-77= 1 1. Then, compare this number with the following cup sizes, and choose the closest size: a difference of 0- 1 inch (about 0-2.54 cm) corresponds to a cup, a difference of 2 inches (about 5.08 cm) corresponds to a cup, a difference of 3 inches (about 7.62 cm) corresponds to a cup, and so on. So according to the data you provided, your underwear cup size may be B or C, and the specific size needs to be carefully tried on and compared with the size tables of different brands. It is recommended to find a professional underwear store or brand when buying underwear, get professional measurement and recommendation, and ensure that the size and wearing of underwear are appropriate.