You can easily look this information up on Harvard's website. There is no required score but it will tell you the range for middle 80% of students from the most recent class. Also, what GMAT score you "need" is highly dependent on the rest of your profile...if you have a 4.0 from a top school, founded a successful company, have significant impactful community service, and clear reasonable post MBA goals you won't "need" as high of a score as someone who has a 3.0 and average work experience.
Also, despite what the 80% range is for HBS if your applying to school you should always ALWAYS just try to get the highest score you possibly can, not focus on just what is "acceptable" by any one program. Harvard is an extremely competitive program so every point you get above their average helps, and depending on your post MBA goals your score can impact your post MBA employment options and scholarship offers.
So basically what I'm saying is..don't worry about what is good enough for any one school, just try to get the best score you can, and apply to schools based on your interest and their fit with who you are and your goals.