Moline987: a regular size condom should be just fine for you.
Sammy444: you can measure girth one of two ways:
1. Take a piece of string and and wrap it once around your penis, mark how much string it takes to go all the way around. Measure this amount using a normal ruler.
2. Get a cloth or vinyl type measuring tape. Wrap it around you penis, as you would the the string. When you do this, 0 will line up with another number, thus giving you your girth size.