From Longman Dictionary of Contemporary Englishweigh somebody/something ↔ up phrasal verb1 THINK ABOUTto consider something carefully so that you can make a decision about it We’re still weighing up the pros and cons (=the advantages and disadvantages) of the two options.2 OPINIONto watch someone and listen to them carefully so that you can form an opinion about what they are like I could see that he was weighing me up. → weigh→ See Verb table
Examples from the Corpus
weigh up• You have to go through a sort of incubation period while people weigh you up.• I can not weigh them up and judge them.• You are not conscious of them weighing you up, but they do.• We weighed each other up for a few moments without speaking.• It doesn't take a brain box to weigh that up - it actually means that 47 people lost their jobs. 