Body Mass Index, or BMI, is commonly used to determine whether or not a person is at a healthy weight. A BMI of 20 to 25 is considered healthy; 25 to 30 represents overweight, while a person with a BMI greater than 30 is said to be obese. These figures are considered to be reliable in most cases, except for the following:

  • Growing children.
  • Elderly people, whose BMI will likely be low due to decreased muscle mass.
  • Serious athletes and body builders, whose BMI will likely be high due to increased muscle mass.
  • Pregnant or lactating women, whose BMI will likely be higher than normal.

Many health experts now believe that BMI may not be a good indicator for many people, since normal people with high BMIs may have low body fat, or vice versa. Waist-to-hip ratio is cited as a more accurate alternative. This is determined by dividing the waist measurement (at the navel) by the hip measurement (at the buttocks). A ratio greater than 0.8 for women, or 0.95 for men, indicates too much belly fat. Read more at this article: When determining who’s fat, is BMI bunk? [Smart Fitness, msnbc.com, May. 1, 2007]

BMI is calculated by dividing the person’s weight in kilograms by the square of his or her height in meters. For U.S. units, multiply the weight in pounds by 703.08, then divide by the square of the height in inches. For those not mathematically inclined, these online calculators will prove useful. They should not, however, substitute for the advice of a qualified health professional.

Calculate Body Mass Index from U.S. units

 

Calculate Body Mass Index from metric units

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