Your icons _must_ be (rounded) squares. You can't use transparency.

JBiserkov · on June 29, 2012

  (rounded) square side = 114px = 2*57
  tau=2pi
  area:= tau*r*r/2
  Chrome:    margin: 16px; radius: 41px = 57-16; area:=  840.5*tau
  Wordpress: margin: 12px; radius: 45px = 57-12; area:= 1012.5*tau
  Clock:     margin:  9px; radius: 48px = 57- 9; area:= 1152.0*tau
  Circle:    margin:  0px; radius: 57px = 57- 0; area:= 1624.5*tau

(Measurments taken from a screenshot on iPod touch "retina" resolution.)

So Chrome's circle area is 73% of Clock's and only 52% of the theoretical limit.

While I was playing with this I got inspired by Google+ for iOS and Metro and asked "What if it doesn't fit, but insead fills the (rounded) square?"

See for yourself. http://biserkov.com/pics/Chrome-on-iOS-icon-ideas.png

Blue circle radius: 21px; White circle radius: 25px

Disclaimer: I used the svg Chrome logo from Wikipedia. I'm no designer.