If you look at this survey: http://www.average-penis-size-chart…enis-girth.html
it looks like over 35% of guys were less than 4.5 inches erect girth.
If you look at the Lifestyles Condoms survey: http://en.wikipedia.org/wiki/File:P…_percentile.svg
it also looks like about 35% of guys were less than or equal to 4.5 inches erect girth.
In this survey, 30% of guys reported a maximum girth of 4.7 inches or less: http://www.sizesurvey.com/result.html but it is a self-reported study and probably the results should be adjusted downward a bit to account for exaggeration.