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BMI and body shape

Tomatoes on the vine

You can tell a lot about your health with simple tools that measure extra body weight. Two of the most helpful are body mass index (BMI) and the shape of your body.

Calculate your BMI

feet on scaleBody mass index (BMI) measures body fat based on your height and weight. It's a quick way to know whether you're at a healthy weight, underweight, overweight, or obese.

In general, the higher your BMI, the greater your risk of developing serious weight-related health problems.

To find out your body mass index, enter your height and weight in our BMI calculator.

Adult BMI falls into the following ranges:

• underweight: less than 18.5
• normal weight: 18.5 to 24.9
• overweight: 25 to 29.9
• obese: 30 and greater

BMI is calculated differently for children and teenagers. Use the BMI calculator for children (ages 2 to 19) to see if your child is at a healthy weight.

What BMI doesn't do

While BMI is part of your health, it does not show the full picture. It's important to keep a few points in mind when thinking about BMI.

• Extra weight may be from dense bone or muscle. A healthy athlete might have very little extra fat, yet still have a BMI in the unhealthy range. Body fat testing is a good way to know whether your extra weight is fat or muscle.
• As we age, we often lose muscle mass and gain fat. An elderly person might fall into the "normal" range, but still have too much body fat because BMI can't tell what's fat and what's muscle.
• Where you carry your extra weight matters, even if you fall into the "normal" range. Belly fat can also show you if you're at risk for serious health issues caused by extra weight.
• Risk factors such as blood pressure, smoking, cholesterol, blood sugar, and medical history are important to keep in mind, even if you have a "normal" BMI.

How do you measure up?

The shape of your body can also tell you if you're at risk for certain types of diseases. You can find out if your body shape puts you at risk with 2 easy tests.

  • Waist-to-hip ratio test. Measure around your waist at your belly button, then measure around your hips at the widest part. Divide your waist size by your hip size. You're more likely to have heart trouble, stroke, diabetes, and other health problems if that number is more than:

men: 0.9 to 1.0
women: 0.8 to 0.9

  • Waist circumference test. Measure around your waist at your belly button. You're at increased risk for the same health problems above if your waist measurement is greater than:

men: 40 inches
women: 35 inches

Reviewed by: Keith Bachman, MD and Trina Histon, PhD, August 2013
Additional Kaiser Permanente reviewers

©2013 Kaiser Permanente