There's no single answer to how many credits are required for a Master's degree in Art History. The credit requirement varies significantly depending on the university, the specific program (e.g., thesis vs. non-thesis), and even the student's chosen specialization within art history.
Generally, you can expect a Master's in Art History to require between 30 and 48 credits, but it's crucial to check the specific requirements on the website of the university and program you're interested in.