BMI is one way to measure for obesity, but not the most accurate. I found this on WebMD 90% or 95% of the population, BMI is just fine as a general measure of obesity," says Richard L. Atkinson, MD, a researcher and editor of the International Journal of Obesity.

But some critics take a different view. Scott Kahan, who directs the National Center for Weight and Wellness, says, "Traditionally, we define obesity by a certain cutoff on the BMI scale." But judging whether a person is obese based only on their size is old-fashioned and not terribly useful, he says.

Some other ways to measure - caliper fold caliper, think Special K pinch an inch.

Bio electric impedance - use of electric current through body.

Anthropometric- Use of different body circumference measurements to estimate body fat.

The most accurate method is hydrostatic weighing which is performed under water.