Body mass index
The body mass index (BMI) is a mathematical formula that healthcare professionals use to correlate a person's height and weight with body fat. The BMI tells whether you're at risk for weight-related illnesses like heart disease, cancer, and diabetes. Your BMI, is your weight (in pounds), divided by your height (in inches) squared. Then this number is multiplied by 705.

Percentage of body fat
Your body weight includes: 1) lean mass, which includes muscles, bones, and organs, and 2) fat. Maintaining the right balance between lean mass and fat is important for health.

It's important to know that muscle mass is heavier than fat. That's why some people—especially athletes and body builders—often show up as overweight on height/weight charts without being over-fat or unhealthy. Conversely, some inactive people may not be overweight in pounds, but they have a high percentage of body fat, which could cause health problems.

There are three common methods for measuring body fat:

• Underwater weighing. Based on the premise that muscle sinks and fat floats, this procedure is done by weighing you while you're submerged in a tank of warm water. Done mostly in sophisticated sports medicine clinics, this method is considered the most accurate.
• Skin-fold caliper measurements. This technique is done using pinchers to pull fat away from your muscles and bones at several body sites and measure its thickness. You can do it yourself at home, but it has a huge margin of error unless done by a professional.
• Bioelectrical impedance. Based on the idea that electricity travels at different rates through fat and lean tissue, this method employs a hand-held device that sends an electrical signal through parts of the body, measuring its speed. It's a handy, inexpensive method, but many experts consider it highly inaccurate.

Even if you don't have your percentage body fat measured, understanding how this ratio affects your health can be helpful, especially as you begin a weight management program. You may gain 5 pounds of muscle mass, for example, at the same time you lose 7 pounds of fat. Although your net loss is just 2 pounds, don't be discouraged. You'll know such changes leave you slimmer and healthier in the long run. A smaller clothing size or waist measurement may be your signals of success.

Waist-to-hip ratio
Maybe you've heard people described as either "apple-shaped" or "pear-shaped." Silly though it may sound, it's an important distinction. Overweight people who carry most of their fat on the abdomen (belly) have a higher risk for weight-related diseases than people who carry most of their fat on the hips and thighs.

Measuring your waist-to-hip ratio is a way to quantify this risk. For women, this ratio should be no greater than 0.80; for men, no greater than 0.95.

To determine your waist-to-hip ratio, measure your waist in inches at the smallest point between your ribcage and navel. Then measure your hips at their largest point around your buttocks. Divide your waist measurement by your hip measurement.

Here are examples: George has a waist of 35 inches and his hips measure 37 inches. Divide his waist measurement (35) by his hip size (37) and you get a WHR of 0.94. Okay for a man. Thelma's waist is 33 inches and her hips are 39. Divide 33 by 39 and you get a WHR of 0.84, a little high for a woman, indicating that Thelma has a higher risk.

Although you can't change where your body tends to carry excess fat, you can work to lessen how much excess fat you carry.

More ways to measure yourself
There's more to weight management than indexes, ratios, and percentages. Here are many other ways to track success:

• noting inches lost around the waist, hips, or thighs
• fitting into a different clothing size
• sticking with a regular exercise program
• having fewer food binges
• making fewer stops for high-fat fast food
• noting lower blood pressure
• noting lower blood cholesterol
• feeling more energetic, confident, and strong
• having more endurance
• finding it easier to perform daily activities like climbing stairs
• suffering less from joint pain
• feeling more comfortable in theater seats, on airplanes, in restaurant booths