Off the top of one's head意思

"Off the top of one's head" is an English idiom that means to answer or state something immediately, without taking the time to think about it or research it. It implies that the response is given quickly and based on one's immediate recall or intuition, rather than on careful consideration or preparation.

For example, someone might say, "I can't remember the exact number off the top of my head, but I think we had about 50 guests at the party." This means that the person is trying to recall the number of guests without taking the time to look at a list or count again.