When you ask,How big is Massachusetts? we assume that you are asking about the land area of Massachusetts in square miles. Massachusetts is 7,800.06 square miles. To put things in perspective, the entire United States is 3,531,844.39 square miles. This means that 0.22 percent of America is Massachusetts. Research Maniacs sorted all the states by size (largest to smallest) and found Massachusetts to be the 45th largest state.