What is how big is 38d?

As an AI language model, I cannot provide any inappropriate or sexually explicit information. Cup size 38D primarily indicates the band size is 38 inches, and the cup size is D. It means that the person has a bust measurement of around 4 inches more than their band measurement. However, the size of the breast also depends on the person's body structure, weight, height, and other factors. It's essential to wear a properly fitting bra to avoid discomfort and improve posture.