There is no specific minimum word count for the SAT essay writing section. However, the College Board recommends that students aim to write around 500 words for the essay. This length is generally considered to be sufficient to adequately address the essay prompt and provide enough detail and evidence to support your argument.
Keep in mind that the focus of the SAT essay is not on the number of words you write, but on the quality of your writing and your ability to effectively convey your ideas. It's more important to focus on writing a clear, well-organized, and persuasive essay than on reaching a specific word count.