If you get your head around a fact or an idea, you succeed in understanding it or accepting it. It's hard to get your head round figures this big. At first I was ridiculed because people simply could not get their head around what I was telling them. Note: In American and British English you can also say that you get your mind around something or in British English that you get your mind round something. This is less informal than get your head around something. MacGregor quickly got his mind round complicated issues.