Raghu, thanx for the link.
I thought I should put a bit of what I picked up from the link here.
"IMPORTANT: Please note that BMI is not as accurate if you are an athlete or very muscled (muscle weighs more than fat), as it can push you into a higher BMI category despite having a healthy level of body fat. It is also not accurate for women who are pregnant or breastfeeding, or people who are frail."
Nevertheless as ratchasi said, it is good enough indicator.