Welcome to English in a Minute,where we teach you all about idioms in American English.What would you think if you heard this:Off the top of my head.There is nothing on her head.But,let's see if we can find out what she means.
A:Do you know Tom's email address?
B:I couldn't tell you off the top of my head,but I have it in my contacts list on my computer.Can I send it to you later?
A:Sure.That would be great.Thanks.
"Off the top of my head"is a common phrase that means I am trying to remember something,and to give you a quick answer.But if a person's memory is bad,sometimes the information off the top of someone's heads is wrong.So it's best to confirm it.
And that's English in a Minute.