There isn’t a single universally agreed count, because historians differ on who qualifies as an emperor, whether co-rulers count, and which usurpers or brief incumbents to include. Estimates typically fall in a range around 40 to 80 named emperors, depending on criteria. Direct answer:

• If you count only the main line of legitimate rulers from Augustus (27 BCE) to Romulus Augustulus (476 CE) and exclude co-emperors and most short-lived usurpers, the count is often given as about 40 to 45 emperors.
• If you include all recognized or semi-recognized rulers, co-emperors, and notable usurpers across the entire Empire (including the Eastern Roman/Byzantine stage up to 1453), counts can rise to roughly 70–100 individuals, depending on source and method.

Key sources commonly cited in overviews include lists of Roman emperors and discussions of legitimacy versus usurpation, which explain why numbers vary. If you’d like, I can pull a concise, cited list of emperors with the counting method (e.g., “mainline only” vs. “including co-emperors and usurpers”) and provide the exact counts from specific historians or reference works.