Nobody knows an actual number, but according to historians, the most likely figure for civilian casualties was around 100,000. That's like 2-3% of the population of the entire continent of North America at that time. That's not including the loyalists who were murdered by the Patriots for their loyalism, which likely numbered several thousand, but below 10,000. An additional 88,000 loyalists fled to the rest of the British Empire, mostly Canada and England, over the course of the war. Interestingly, since most empires and nations had entirely unrestricted immigration up until the 20th century, the concept of refugees never really existed until World War I so these loyalists who fleed were not considered refugees.