Off the top of one's head

From Fresh Dictionary

English

Adverb

off the top of one's head

1. ((idiomatic{{#if:|, {{{2}}}{{#if:|, {{{3}}}{{#if:|, {{{4}}}{{#if:|, {{{5}}}{{#if:|, {{{6}}}{{#if:|, {{{7}}}{{#if:|, {{{8}}}{{#if:|, {{{9}}}}}}}}}}}}}}}}}}})) (of something known, thought of, or remembered) Without great thought or investigation; extemporaneous; natural; offhand.

   I cannot think of any good examples off the top of my head, but give me a couple of hours and I'm sure I could come up with something.

ru:off the top of one's head