off the top of your head
US /ɔf ðə tɑp əv jʊər hɛd/
UK /ɔf ðə tɑp əv jʊər hɛd/

1.
a memoria, su due piedi
from memory, without careful thought or checking facts
:
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I can't tell you the exact number off the top of my head, but it's around fifty.
Non posso dirti il numero esatto a memoria, ma è circa cinquanta.
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Can you name three capital cities off the top of your head?
Puoi nominare tre capitali a memoria?