Knowing your body mass index or BMI can be helpful in assessing and adjusting your weight. Keep in mind that this is not the most accurate measure of how much body fat you have, but rather the easiest and least expensive way to measure it. There are different ways to calculate your BMI depending on the type of measurements you have taken. Make sure you know your current height and weight before proceeding to calculate your BMI.
Go to step When should you try to do this? to learn more about when calculating your BMI is the best option.
Method 1 of 4: Use metric measurements
Step 1. Measure your height in meters and square the number
To achieve this, you must first multiply your height in meters by itself. For example, if you are 1.75 meters tall, then you would multiply 1.75 by 1.75 and get an approximate result of 3.06.
Step 2. Divide your weight in kilograms by the square meters
Then, you must divide your weight in kilograms by your height expressed in square meters. For example, if your weight is 75 kilograms and your height in square meters is 3.06, then you would divide 75 by 3.06 to get a resulting BMI of 24.5.
Step 3. Use an extended equation if you have measured your height in centimeters
It is still possible to calculate your BMI if your height is in centimeters, but you will need to use a slightly different equation to do so. This equation consists of taking your weight in kilograms and dividing it by your height in centimeters and then dividing the result by your height in centimeters and finally multiplying the result by 10,000.
For example, if your weight in kilograms is 60 and your height in centimeters is 152, then you would divide 60 by 152, by 152 (60/152/152) to get a result of 0.002596. Then multiply this number by 10,000 and you will get a result of 25, 96 or approximately 30. The approximate BMI for this person would be 30
Method 2 of 4: Use Imperial Measurements
Step 1. Square your height in inches
To do this, multiply your height in inches by itself. For example, if you are 70 inches tall, then you would multiply 70 by 70. Your answer for this example would be 4900.
Step 2. Divide your weight by your height
Next, you will need to divide your weight by your height in inches squared. For example, if your weight in pounds is 180, then you would divide 180 by 4900. Your answer for this example would be 0.03673.
Step 3. Multiply that answer by 703
To get your BMI, you would multiply your last answer by 703. For example, 0.03673 times 703 equals 25.82, so your approximate BMI for this example would be 25.8.
Method 3 of 4: Use the metric conversion factor
Step 1. Multiply your height in inches by 0.025
This number is the metric conversion factor needed to convert inches to meters. For example, if your height is 60 inches, then you would multiply 60 by 0.025 to get a result of 1.5 meters.
Step 2. Square your last result
Next, you need to multiply your last result by itself. For example, if the last number you got was 1, 5, then you would multiply 1, 5 by 1, 5. In this situation, your answer would be 2, 25.
Step 3. Multiply your weight in pounds by 0.45
This number is the metric conversion factor needed to convert pounds to kilograms. This will convert your weight to its metric equivalent. For example, if your weight is 150 pounds, then your answer would be 67, 5.
Step 4. Divide the larger number by the smaller number
Take the result you get for your weight and divide it by the result you got for your height squared. For example, you would divide 67.5 by 2.25. The answer will be your BMI, which in this example would be 30.
Method 4 of 4: When should you try doing this?
Step 1. Calculate your BMI to determine if your weight is healthy
Your BMI is important because it can help you determine if your weight is underweight, normal, overweight, or obese.
- A BMI below 18.5 means that your weight is below the appropriate weight.
- A BMI between 18, 6 and 24, 9 means that your weight is healthy.
- A BMI between 25 and 29.9 means you are overweight.
- A BMI of 30 or more indicates the presence of obesity.
Step 2. Use your BMI to determine if you are suitable for bariatric surgery
In some situations, your BMI will be required to be above a certain number in order for you to undergo bariatric surgery. For example, to qualify for bariatric surgery in the UK, your BMI must be 35 or higher if you do not have diabetes and at least 30 if you have diabetes.
Step 3. Track changes in your BMI over time
You can also use your BMI to track changes in your weight. For example, if you want to create a weight loss chart, then calculating your BMI on a regular basis could be helpful. On the other hand, if you want to track your or your child's growth, then calculating and tracking BMI is another way to do it.
Step 4. Calculate the BMI before considering other more expensive and invasive options
If with the help of the BMI you can determine that your body weight is in a healthy range, then this could be the best option. However, if you are an athlete or sports enthusiast and you think that your BMI gives you an inaccurate picture of your body's fat content, then you could use a different option.
Skinfold testing, hydrostatic weight, dual energy X-ray absorptiometry (DXA), and bioelectrical impedance are other options available to determine your body's fat content. You just have to keep in mind that these methods are more expensive and invasive than calculating BMI
- Maintaining a healthy weight is perhaps the only important step you can take to achieve optimal health and a long life. BMI is simply an indicator of your general condition and physical health.
- Another easy way to determine if your weight is healthy is to calculate your waist-to-hip ratio.