know at a glance that
know at a glance that (something is the case)
To understand or realize very quickly that something is the case, without the need for much evidence or careful consideration. The mechanic knew at a glance that the engine was beyond repair. My dad knew at a glance that we were lying about what happened.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
know at a glance that...
to know [something] without much evidence; to know or understand something without a lot of observation. I knew at a glance that Bobbie was severely injured and had to be gotten to a hospital as soon as possible.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.