off the top of my head 文字上的意思是"只從我頭上", 也就是"我一時(只用想)的..."的意思, 但不是"一時之間記不起來"哦.
Eric: Hey W, can you remember how many times we've been to New York together?
Eric: 嘿, W, 你記不記得我們一起去過幾次紐約?
W: Off the top of my head, probably five times. But I can check on it.
W: 我(不用查)現在想, 應該五次吧. 我可以去查查看
W: How many years have you been an accountant?
W: 你當多久會計師了呢?
J: Oh, fifteen years six months and twelve days.
J: 嗯, 十五年六個月又十二天
W: How did you manage to do that, just off the top of your head?
W: 你怎麼那麼利害, 難道你(不用想)直接就能算出來?
J: I am an accountant, we're good at counting
J: 我是個會計師, 我們都很會算數的