Body Mass Index, or BMI, is a quick and easy way to estimate how much body fat you may have based on your weight and height. If you’re wondering how to calculate bmi metric, it involves dividing your weight in kilograms by the square of your height in meters. It’s commonly used to check if your weight falls into a healthy range and to estimate your risk for health conditions like heart disease, diabetes, or high blood pressure.
How BMI Is Calculated
You can calculate your BMI using two different systems. With the metric system, the formula is:
BMI = weight (kg) ÷ height (m²)
With the imperial system, the formula is:
BMI = (weight in pounds ÷ [height in inches × height in inches]) × 703
Here are two examples:
- If someone weighs 75 kilograms and is 1.75 meters tall, you square the height: 1.75 × 1.75 = 3.06. Then divide 75 by 3.06. The BMI is 24.5.
- If a person weighs 180 pounds and is 70 inches tall, first square the height: 70 × 70 = 4,900. Then divide the weight by the squared height: 180 ÷ 4,900. Finally, multiply that result by 703 to get the BMI. The BMI is 25.8.
You can also use many online tools and apps to do the calculations for you.
What Your BMI Score Means
BMI numbers are grouped into categories to help understand your weight status:
- Below 18.5 means you may be underweight
- 5 to 24.9 is considered a healthy weight
- 25 to 29.9 is in the overweight range
- 30 or more fall into the obesity range
Obesity is sometimes broken down further:
Class 1 (30–34.9), Class 2 (35–39.9), and Class 3 (40 or higher), also known as severe obesity.
How BMI Relates to Health
A high BMI can raise the risk of several health issues, including heart disease, sleep apnea, type 2 diabetes, high cholesterol, and some types of cancer. However, BMI is not a perfect tool and doesn’t always reflect how healthy or unhealthy a person is.
Limitations of BMI
BMI does not take into account muscle mass, age, sex, or ethnic background. For example:
- Athletes might show a high BMI due to having more muscle rather than excess fat.
- Older adults, on the other hand, may have a normal BMI but still carry unhealthy levels of body fat.
- People of Asian or South Asian descent may face health risks at lower BMI levels
- Women naturally carry more body fat than men
Better Tools to Measure Health
Besides BMI, other useful tools include waist measurements, waist-to-hip ratios, and body fat tests using callipers or smart scales. More advanced methods, like DEXA scans or underwater weighing, can measure fat and muscle more accurately but are often used in research settings.
Summary
BMI is a quick and simple way to check if your weight might be putting your health at risk. While useful, it has limits and doesn’t give a full picture. To truly understand your health, BMI should be used alongside other tests and under the guidance of a healthcare provider.
