Figuring out one's body mass index (BMI) is complicated. And many people are only interested in part of what it means—their highest healthy weight. A professor at the University of Nevada, Reno has analyzed BMI charts and come up with a simple way for people to find their maximum healthy weight.

In other words, this is as high as your weight can go before you're overweight.

Hernandez felt people needed a single number, like a speed limit, rather than a healthy weight range.

According to these new guidelines:

  • For a 5−foot, 9−inch tall man, the maximum healthy weight is 175 pounds. Ideal weight rises by 5 pounds per inch for taller men and drops 5 pounds per inch for shorter men. This gives a maximum healthy weight of 200 pounds if you're 6 feet 2, 150 pounds if you're 5' 4".

  • For a 5−foot tall woman, the ideal weight is 125 pounds, and it changes by 4.5 pounds for every inch of height above or below 5 feet. So, if you are 5' 4", your ideal weight is 125 + (4 x 4.5) =143 pounds.

These figures correspond to a BMI of 25.5 for men and 24.5 for women. The difference is intentional; it takes into account the fact that men generally have more muscle mass than women. A BMI of 25 is usually taken to be the top of the healthy range.

In contrast, to calculate your BMI, you'd have to multiply your weight in pounds by 703, and then divide the product by your height in inches, squared. Then you'd have to look up that BMI on a chart to see where it stands.

George Fernandez, a professor of applied statistics and director of the Center for Research Design and Analysis at the University of Nevada, Reno, came up with the new calculation. Hernandez felt people needed a single number, like a speed limit, rather than a healthy weight range. He also wanted to give people a calculation that didn't rely on the use of a chart or calculator. Using statistical software, he was able to take the information in BMI charts and extract the part that many people want to know: the maximum healthy weight for any given height. He calls it a Maximum Weight Limit.

While individuals of the same height do vary in weight, being different in muscle or bone mass, BMI has been shown to accurately give a healthy weight for over 90% of the population. And Fernandez' maximum healthy weight figures come from BMI calculations; they're just expressed a lot more simply.

The research was scheduled to be presented at the Nevada Public Health Association conference on September 22, 2009 at the University of Nevada.