The Body Mass Index (BMI) is a measurement tool that compares your height to your weight and gives you an indication of whether you are overweight, underweight or at a healthy weight for your height. For details on calculating your BMI manually, follow the steps below.
Weigh & Measure
Weigh yourself on your bathroomscale. Note: the following formula is calculated in pounds.
Measure your height in inches using the yardstick or measuring tape. Stand against the wall and use a pencil to make a mark at the top of your head, then measure.
Calculating Your BMI Manually
Use the pencil, paper and calculator to perform the following BMI calculation.
Take your height in inches and square the number. In other words, multiply the number of inches by the same number of inches.
Divide your weight in pounds by the second figure. The second figure is your height in inches squared.
Multiply that answer by the conversion factor of 703 if you used inches and pounds. Skip if you used meters and kilograms. The answer is your body mass index.
Judge your personal BMI result against the following scale:
• A BMI of less than 18 means you are under weight.
• A BMI of less than 18.5 indicates you are thin for your height.
• A BMI between 18.6 and 24.9 indicates you are at a healthy weight.
• A BMI between 25 and 29.9 suggests you are overweight for your height.
• A BMI of 30 or greater indicates obesity. If you are obese, consider consulting a doctor or losing weight.
• Maintaining a healthy weight is perhaps the single most important step you can take toward optimal health and long life. Calculating your BMI is a good rough indicator of your current weight and general condition.
• The exact multiplicative factor is actually 703 + (4489/64516), but the tiny difference (about 0.002 in the BMI) is fully negligible.
• Recent research has found that the waist to hip ratio provides a much better indicator than BMI of whether an individual has too much body fat. Generally the waist to hip ratio should not exceed about 0.9 for men and 0.8 for women. Higher ratios indicate an increased risk of stroke, diabetes, and heart attack.
• The BMI is a pretty good indicator for the average person from age 25 to 65. But it has its limitations. It does not take into account muscle mass or your overall body type ("apple" vs. "pear" body types).
• BMI is actually just a guideline and should not be used if one has access to a Skinfold test or a BIA (Bio-electrical impedance analysis). These tests measure the total amount of body weight that is from fat. This method is far more accurate and readily available at most gyms. Some home BIA tests are available via scales that also measure BIA. There are other methods that have a lower variance but are expensive, invasive and difficult to perform.