"Form an estimate of" is a phrase commonly used to refer to the act of making a judgment or prediction about something based on available information. However, there are several other phrases that can also be used to convey this meaning. Some synonyms for "form an estimate of" include "make a guess at", "gauge", "assess", "predict", "approximate", "evaluate", "estimate", "calculate" and "determine". Each of these phrases suggests a slightly different approach or level of certainty, and so the choice of word may depend on the context and the desired tone of the communication.