The condom industry has some weird standards. First, condom sizes refer to the width of the flattened condom, not its diameter, so "pi" doesn't apply. The width of a flattened circle is 1/2 its circumference (girth). So, theoretically, if your girth is 5.55 inches, your condom size would be 5.55/2 inches x 25.4 mm/inch = 70 mm. But buying a size by this method will result in a loose fit. I'd recommend at least 10% smaller (which would make it 63 mm instead, because you need the condom to stretch a bit for a snug, but not tight, fit. "My Size" condoms (German, I think) makes sizes up to 72 or 74 mm if memory serves.
I'm 6.25" in girth, which technically computes to a condom size of 79 mm, but I get a great fit with 69 mm condoms.