When expressing certainty or confidence about something, there are several synonyms for the phrase "are sure about." These include "are certain," "are confident," "are convinced," "are positive," "are secure," "are unshakable," "are steadfast," "are resolute," "are undoubting," and "are adamant." Each of these phrases conveys a sense of unwavering belief or assurance in one's knowledge or opinion on a matter. Using synonyms can add variety and depth to your language, making your writing or speech more engaging and impactful. Whatever synonym you choose, be sure to use it with conviction and clarity.