The answer is 1 in 5 American colonists.
Now it may look like that the decision to start a revolution in the US in 1776 was an easy one. But it was not so. Roughly one third of the population was for the revolution, one third against it and one third was undecided. A major factor in convincing the undecided colonists was Thomas Paine's Common Sense pamphlet which converted many to the revolutionaries cause. So about 1 in 5 colonists remained loyal to the British Crown and they were known as the Loyalists.