From Longman Dictionary of Contemporary Englishsize somebody/something ↔ up phrasal verbJUDGEto look at or consider a person or situation and make a judgment about them SYN assess It only took a few seconds for her to size up the situation. → size→ See Verb table
Examples from the Corpus
size up• Over time, our average order size is going up.• They stood looking at one another like two cats sizing each other up.• Of single size with metal up and over door.• It was partly for a story, and partly to size the paper up as competition or business.• Most are in primary schools where the average class size has shot up from 26.1 to 28.8 in two years.• He had sized me up, he later explained, and had decided to take me under his wing.• But what they lack in size they make up in numbers.• This consisted of drawing on graph paper ten figures of slightly varying geometric size, made up of squares. 