iBodyFat is an application which calculates your body fat percentage and keeps a log of your results. Two different calculations are presented for each measurement made. The body fat percentage formulas used by iBodyFat are girth body fat calculations invented by the U.S. Navy, and professional body builder and writer Hugo Rivera.
For taking girth body fat measurements, no special equipment is needed; all that is required is a vinyl tape measure. Girth is not as accurate as skin fold techniques using body fat calipers, but there has been claim of within 3% accuracy. There is chance it can be wrong in some people because you can only tell so much by circumference, but this will be the best you can do without using expensive equipment.