a mile off

a mile off

Very easily. Always of something detected or observed. I can spot Paul a mile off, just by the way he walks. After decades as an investigator, I can identify a con man a mile off.
See also: mile, off
Farlex Dictionary of Idioms.

a mile off

or

a mile away

INFORMAL
If you can see something or someone a mile off or a mile away, you can notice or recognize them very easily. You can spot undercover cops a mile off. I can tell a wig a mile off. He knew Ann could spot a lie a mile away.
See also: mile, off
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • a mile away
  • miles away
  • by a mile
  • run a mile
  • private eye
  • a private eye
  • cast
  • cast (some) light on (something)
  • cast/shed/throw light on something
  • throw (some) light on (something)
References in classic literature
But the shot passed some feet above the cetacean, which was half a mile off.
20000 Leagues Under The Sea