Do a thorough census, and subtract that number from the population they had before the invasion, which was probably fairly accurate, and then you'd get at least a reasonable ballpark figure.

I don't think we'll ever really know with any degree of accuracy. But since it's politically advantageous for both the U.S. military and the Iraqi government to downplay the number of deaths, they probably are. The real number is probably somewhere between the two extremes. And whatever number it is, it's a lot, percentage-wise. If I lived in Iraq, I'd be doing nothing but trying to figure out how to get the hell out of there and find a safer place to live.