Expressions used in Everyday Spoken English in Social and Professional contexts
When you 'size up' a person or a situation you evaluate the person or situation in order to decide what you think and how to act. Similarly 'to measure someone up' means to assess someone carefully or to make a judgement about them. To 'measure someone up' can also mean to literally take measurements of their body in order to make or fit clothing specifically for them. Don't confuse this with 'to measure up to someone' which means to be equally as good as or successful as someone else.