the size=尺码,尺寸.(指比较精确的数字) How big=大小.(通常用来泛指一个物件的大小) What is the size of the shirt?这件衬衫是甚麼尺码? -->也可以说:(How big is the shirt?这件衬衫有多大?) This shirt is your size.这件衬衫是你的尺码. What is your size?你(穿衣服)的尺码是多大? -->也可以说:(How big do you need?你需要的尺寸是多大?) I will size up the shirt.我要估算一下这件衬衫的大小. 以上供您参考,