There is no official minimum, and schools say clearly that they weigh depth and consistency over a magic number. That said, here are the ranges applicants actually cite. Clinical experience: many competitive applicants report 200 or more hours, and more is common. Shadowing: roughly 40 to 50 hours, ideally spread across a few specialties, and including time with a DO if you plan to apply osteopathic.
Non-clinical volunteering: sustained service you genuinely care about, often 100 or more hours. Research: expected at many research-heavy schools and far less so elsewhere, where real depth in one project beats a semester spent drifting through three.
The pattern that helps most is commitment over time. A weekly role you hold for a year or two reads far better than a frantic sprint the summer before you apply. Start early, keep a simple log of hours and contacts, and let the totals build on their own.