Quite frankly, my own estimation. Kinsey went as high as 10% but more recent studies seem to favor 3-7%. My guesstimate is based on the number of "straight" men I've seen on hook-up websites and sucking my cock in adult book stores. I know straight away there is no survey in the world that will make these guys admit they're gay, but there they are on their knees or with their asses in the air and a wedding band on their finger. It's sad but true.