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.
Note: The following formula is calculated in pounds. You will need your current weight and height.
How to Calculate BMI:
- 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.
- Multiply that answer by the conversion factor of 703 (Note: This is only if you using inches and pounds). The answer is your body mass index.
- Someone who is 70 inches tall and 180 pounds:
- 70 x 70 = 4,900.
- 180 / 4,900 = 0.036734693
- 0.036734693 x 703 = 25.82
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.
Tips and Why Calculating Your BMI is Important:
- Maintaining a healthy weight is perhaps the single most important step you can take toward optimal health and a long life. Calculating your BMI is a good rough indicator of your general condition.
- The exact multiplicative factor in calculating BMI is actually 703 + (4489/64516), but the tiny difference (about 0.002 in the BMI) is fully negligible.
- 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.
- 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.
Adapted from How to Calculate Your Body Mass Index (BMI).